/*
 * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 *
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 *
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 *
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 *
 *
 *
 *
 */

package java.util.regex;

import java.text.Normalizer;
import java.util.Locale;
import java.util.Iterator;
import java.util.Map;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Arrays;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Predicate;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;


/**
 * A compiled representation of a regular expression.
 *
 * <p> A regular expression, specified as a string, must first be compiled into an instance of this
 * class.  The resulting pattern can then be used to create a {@link Matcher} object that can match
 * arbitrary {@linkplain java.lang.CharSequence character sequences} against the regular expression.
 *  All of the state involved in performing a match resides in the matcher, so many matchers can
 * share the same pattern.
 *
 * <p> A typical invocation sequence is thus
 *
 * <blockquote><pre>
 * Pattern p = Pattern.{@link #compile compile}("a*b");
 * Matcher m = p.{@link #matcher matcher}("aaaaab");
 * boolean b = m.{@link Matcher#matches matches}();</pre></blockquote>
 *
 * <p> A {@link #matches matches} method is defined by this class as a convenience for when a
 * regular expression is used just once.  This method compiles an expression and matches an input
 * sequence against it in a single invocation.  The statement
 *
 * <blockquote><pre>
 * boolean b = Pattern.matches("a*b", "aaaaab");</pre></blockquote>
 *
 * is equivalent to the three statements above, though for repeated matches it is less efficient
 * since it does not allow the compiled pattern to be reused.
 *
 * <p> Instances of this class are immutable and are safe for use by multiple concurrent threads.
 * Instances of the {@link Matcher} class are not safe for such use.
 *
 *
 * <h3><a name="sum">Summary of regular-expression constructs</a></h3>
 *
 * <table border="0" cellpadding="1" cellspacing="0" summary="Regular expression constructs, and
 * what they match">
 *
 * <tr align="left"> <th align="left" id="construct">Construct</th> <th align="left"
 * id="matches">Matches</th> </tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="characters">Characters</th></tr>
 *
 * <tr><td valign="top" headers="construct characters"><i>x</i></td> <td headers="matches">The
 * character <i>x</i></td></tr> <tr><td valign="top" headers="construct characters"><tt>\\</tt></td>
 * <td headers="matches">The backslash character</td></tr> <tr><td valign="top" headers="construct
 * characters"><tt>\0</tt><i>n</i></td> <td headers="matches">The character with octal value
 * <tt>0</tt><i>n</i> (0&nbsp;<tt>&lt;=</tt>&nbsp;<i>n</i>&nbsp;<tt>&lt;=</tt>&nbsp;7)</td></tr>
 * <tr><td valign="top" headers="construct characters"><tt>\0</tt><i>nn</i></td> <td
 * headers="matches">The character with octal value <tt>0</tt><i>nn</i>
 * (0&nbsp;<tt>&lt;=</tt>&nbsp;<i>n</i>&nbsp;<tt>&lt;=</tt>&nbsp;7)</td></tr> <tr><td valign="top"
 * headers="construct characters"><tt>\0</tt><i>mnn</i></td> <td headers="matches">The character
 * with octal value <tt>0</tt><i>mnn</i> (0&nbsp;<tt>&lt;=</tt>&nbsp;<i>m</i>&nbsp;<tt>&lt;=</tt>&nbsp;3,
 * 0&nbsp;<tt>&lt;=</tt>&nbsp;<i>n</i>&nbsp;<tt>&lt;=</tt>&nbsp;7)</td></tr> <tr><td valign="top"
 * headers="construct characters"><tt>\x</tt><i>hh</i></td> <td headers="matches">The character with
 * hexadecimal&nbsp;value&nbsp;<tt>0x</tt><i>hh</i></td></tr> <tr><td valign="top"
 * headers="construct characters"><tt>&#92;u</tt><i>hhhh</i></td> <td headers="matches">The
 * character with hexadecimal&nbsp;value&nbsp;<tt>0x</tt><i>hhhh</i></td></tr> <tr><td valign="top"
 * headers="construct characters"><tt>&#92;x</tt><i>{h...h}</i></td> <td headers="matches">The
 * character with hexadecimal&nbsp;value&nbsp;<tt>0x</tt><i>h...h</i> ({@link
 * java.lang.Character#MIN_CODE_POINT Character.MIN_CODE_POINT} &nbsp;&lt;=&nbsp;<tt>0x</tt><i>h...h</i>&nbsp;&lt;=&nbsp;
 * {@link java.lang.Character#MAX_CODE_POINT Character.MAX_CODE_POINT})</td></tr> <tr><td
 * valign="top" headers="matches"><tt>\t</tt></td> <td headers="matches">The tab character
 * (<tt>'&#92;u0009'</tt>)</td></tr> <tr><td valign="top" headers="construct
 * characters"><tt>\n</tt></td> <td headers="matches">The newline (line feed) character
 * (<tt>'&#92;u000A'</tt>)</td></tr> <tr><td valign="top" headers="construct
 * characters"><tt>\r</tt></td> <td headers="matches">The carriage-return character
 * (<tt>'&#92;u000D'</tt>)</td></tr> <tr><td valign="top" headers="construct
 * characters"><tt>\f</tt></td> <td headers="matches">The form-feed character
 * (<tt>'&#92;u000C'</tt>)</td></tr> <tr><td valign="top" headers="construct
 * characters"><tt>\a</tt></td> <td headers="matches">The alert (bell) character
 * (<tt>'&#92;u0007'</tt>)</td></tr> <tr><td valign="top" headers="construct
 * characters"><tt>\e</tt></td> <td headers="matches">The escape character
 * (<tt>'&#92;u001B'</tt>)</td></tr> <tr><td valign="top" headers="construct
 * characters"><tt>\c</tt><i>x</i></td> <td headers="matches">The control character corresponding to
 * <i>x</i></td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="classes">Character
 * classes</th></tr>
 *
 * <tr><td valign="top" headers="construct classes">{@code [abc]}</td> <td headers="matches">{@code
 * a}, {@code b}, or {@code c} (simple class)</td></tr> <tr><td valign="top" headers="construct
 * classes">{@code [^abc]}</td> <td headers="matches">Any character except {@code a}, {@code b}, or
 * {@code c} (negation)</td></tr> <tr><td valign="top" headers="construct classes">{@code
 * [a-zA-Z]}</td> <td headers="matches">{@code a} through {@code z} or {@code A} through {@code Z},
 * inclusive (range)</td></tr> <tr><td valign="top" headers="construct classes">{@code
 * [a-d[m-p]]}</td> <td headers="matches">{@code a} through {@code d}, or {@code m} through {@code
 * p}: {@code [a-dm-p]} (union)</td></tr> <tr><td valign="top" headers="construct classes">{@code
 * [a-z&&[def]]}</td> <td headers="matches">{@code d}, {@code e}, or {@code f} (intersection)</tr>
 * <tr><td valign="top" headers="construct classes">{@code [a-z&&[^bc]]}</td> <td
 * headers="matches">{@code a} through {@code z}, except for {@code b} and {@code c}: {@code [ad-z]}
 * (subtraction)</td></tr> <tr><td valign="top" headers="construct classes">{@code
 * [a-z&&[^m-p]]}</td> <td headers="matches">{@code a} through {@code z}, and not {@code m} through
 * {@code p}: {@code [a-lq-z]}(subtraction)</td></tr> <tr><th>&nbsp;</th></tr>
 *
 * <tr align="left"><th colspan="2" id="predef">Predefined character classes</th></tr>
 *
 * <tr><td valign="top" headers="construct predef"><tt>.</tt></td> <td headers="matches">Any
 * character (may or may not match <a href="#lt">line terminators</a>)</td></tr> <tr><td
 * valign="top" headers="construct predef"><tt>\d</tt></td> <td headers="matches">A digit:
 * <tt>[0-9]</tt></td></tr> <tr><td valign="top" headers="construct predef"><tt>\D</tt></td> <td
 * headers="matches">A non-digit: <tt>[^0-9]</tt></td></tr> <tr><td valign="top" headers="construct
 * predef"><tt>\h</tt></td> <td headers="matches">A horizontal whitespace character: <tt>[
 * \t\xA0&#92;u1680&#92;u180e&#92;u2000-&#92;u200a&#92;u202f&#92;u205f&#92;u3000]</tt></td></tr>
 * <tr><td valign="top" headers="construct predef"><tt>\H</tt></td> <td headers="matches">A
 * non-horizontal whitespace character: <tt>[^\h]</tt></td></tr> <tr><td valign="top"
 * headers="construct predef"><tt>\s</tt></td> <td headers="matches">A whitespace character: <tt>[
 * \t\n\x0B\f\r]</tt></td></tr> <tr><td valign="top" headers="construct predef"><tt>\S</tt></td> <td
 * headers="matches">A non-whitespace character: <tt>[^\s]</tt></td></tr> <tr><td valign="top"
 * headers="construct predef"><tt>\v</tt></td> <td headers="matches">A vertical whitespace
 * character: <tt>[\n\x0B\f\r\x85&#92;u2028&#92;u2029]</tt> </td></tr> <tr><td valign="top"
 * headers="construct predef"><tt>\V</tt></td> <td headers="matches">A non-vertical whitespace
 * character: <tt>[^\v]</tt></td></tr> <tr><td valign="top" headers="construct
 * predef"><tt>\w</tt></td> <td headers="matches">A word character: <tt>[a-zA-Z_0-9]</tt></td></tr>
 * <tr><td valign="top" headers="construct predef"><tt>\W</tt></td> <td headers="matches">A non-word
 * character: <tt>[^\w]</tt></td></tr> <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2"
 * id="posix"><b>POSIX character classes (US-ASCII only)</b></th></tr>
 *
 * <tr><td valign="top" headers="construct posix">{@code \p{Lower}}</td> <td headers="matches">A
 * lower-case alphabetic character: {@code [a-z]}</td></tr> <tr><td valign="top" headers="construct
 * posix">{@code \p{Upper}}</td> <td headers="matches">An upper-case alphabetic character:{@code
 * [A-Z]}</td></tr> <tr><td valign="top" headers="construct posix">{@code \p{ASCII}}</td> <td
 * headers="matches">All ASCII:{@code [\x00-\x7F]}</td></tr> <tr><td valign="top" headers="construct
 * posix">{@code \p{Alpha}}</td> <td headers="matches">An alphabetic character:{@code
 * [\p{Lower}\p{Upper}]}</td></tr> <tr><td valign="top" headers="construct posix">{@code
 * \p{Digit}}</td> <td headers="matches">A decimal digit: {@code [0-9]}</td></tr> <tr><td
 * valign="top" headers="construct posix">{@code \p{Alnum}}</td> <td headers="matches">An
 * alphanumeric character:{@code [\p{Alpha}\p{Digit}]}</td></tr> <tr><td valign="top"
 * headers="construct posix">{@code \p{Punct}}</td> <td headers="matches">Punctuation: One of {@code
 * !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~}</td></tr> <!-- {@code [\!"#\$%&'\(\)\*\+,\-\./:;\<=\>\?@\[\\\]\^_`\{\|\}~]}
 * {@code [\X21-\X2F\X31-\X40\X5B-\X60\X7B-\X7E]} --> <tr><td valign="top" headers="construct
 * posix">{@code \p{Graph}}</td> <td headers="matches">A visible character: {@code
 * [\p{Alnum}\p{Punct}]}</td></tr> <tr><td valign="top" headers="construct posix">{@code
 * \p{Print}}</td> <td headers="matches">A printable character: {@code [\p{Graph}\x20]}</td></tr>
 * <tr><td valign="top" headers="construct posix">{@code \p{Blank}}</td> <td headers="matches">A
 * space or a tab: {@code [ \t]}</td></tr> <tr><td valign="top" headers="construct posix">{@code
 * \p{Cntrl}}</td> <td headers="matches">A control character: {@code [\x00-\x1F\x7F]}</td></tr>
 * <tr><td valign="top" headers="construct posix">{@code \p{XDigit}}</td> <td headers="matches">A
 * hexadecimal digit: {@code [0-9a-fA-F]}</td></tr> <tr><td valign="top" headers="construct
 * posix">{@code \p{Space}}</td> <td headers="matches">A whitespace character: {@code [
 * \t\n\x0B\f\r]}</td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2">java.lang.Character classes (simple <a
 * href="#jcc">java character type</a>)</th></tr>
 *
 * <tr><td valign="top"><tt>\p{javaLowerCase}</tt></td> <td>Equivalent to
 * java.lang.Character.isLowerCase()</td></tr> <tr><td valign="top"><tt>\p{javaUpperCase}</tt></td>
 * <td>Equivalent to java.lang.Character.isUpperCase()</td></tr> <tr><td
 * valign="top"><tt>\p{javaWhitespace}</tt></td> <td>Equivalent to java.lang.Character.isWhitespace()</td></tr>
 * <tr><td valign="top"><tt>\p{javaMirrored}</tt></td> <td>Equivalent to
 * java.lang.Character.isMirrored()</td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="unicode">Classes for Unicode
 * scripts, blocks, categories and binary properties</th></tr> <tr><td valign="top"
 * headers="construct unicode">{@code \p{IsLatin}}</td> <td headers="matches">A Latin&nbsp;script
 * character (<a href="#usc">script</a>)</td></tr> <tr><td valign="top" headers="construct
 * unicode">{@code \p{InGreek}}</td> <td headers="matches">A character in the Greek&nbsp;block (<a
 * href="#ubc">block</a>)</td></tr> <tr><td valign="top" headers="construct unicode">{@code
 * \p{Lu}}</td> <td headers="matches">An uppercase letter (<a href="#ucc">category</a>)</td></tr>
 * <tr><td valign="top" headers="construct unicode">{@code \p{IsAlphabetic}}</td> <td
 * headers="matches">An alphabetic character (<a href="#ubpc">binary property</a>)</td></tr> <tr><td
 * valign="top" headers="construct unicode">{@code \p{Sc}}</td> <td headers="matches">A currency
 * symbol</td></tr> <tr><td valign="top" headers="construct unicode">{@code \P{InGreek}}</td> <td
 * headers="matches">Any character except one in the Greek block (negation)</td></tr> <tr><td
 * valign="top" headers="construct unicode">{@code [\p{L}&&[^\p{Lu}]]}</td> <td
 * headers="matches">Any letter except an uppercase letter (subtraction)</td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="bounds">Boundary
 * matchers</th></tr>
 *
 * <tr><td valign="top" headers="construct bounds"><tt>^</tt></td> <td headers="matches">The
 * beginning of a line</td></tr> <tr><td valign="top" headers="construct bounds"><tt>$</tt></td> <td
 * headers="matches">The end of a line</td></tr> <tr><td valign="top" headers="construct
 * bounds"><tt>\b</tt></td> <td headers="matches">A word boundary</td></tr> <tr><td valign="top"
 * headers="construct bounds"><tt>\B</tt></td> <td headers="matches">A non-word boundary</td></tr>
 * <tr><td valign="top" headers="construct bounds"><tt>\A</tt></td> <td headers="matches">The
 * beginning of the input</td></tr> <tr><td valign="top" headers="construct bounds"><tt>\G</tt></td>
 * <td headers="matches">The end of the previous match</td></tr> <tr><td valign="top"
 * headers="construct bounds"><tt>\Z</tt></td> <td headers="matches">The end of the input but for
 * the final <a href="#lt">terminator</a>, if&nbsp;any</td></tr> <tr><td valign="top"
 * headers="construct bounds"><tt>\z</tt></td> <td headers="matches">The end of the input</td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="lineending">Linebreak
 * matcher</th></tr> <tr><td valign="top" headers="construct lineending"><tt>\R</tt></td> <td
 * headers="matches">Any Unicode linebreak sequence, is equivalent to
 * <tt>&#92;u000D&#92;u000A|[&#92;u000A&#92;u000B&#92;u000C&#92;u000D&#92;u0085&#92;u2028&#92;u2029]
 * </tt></td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="greedy">Greedy
 * quantifiers</th></tr>
 *
 * <tr><td valign="top" headers="construct greedy"><i>X</i><tt>?</tt></td> <td
 * headers="matches"><i>X</i>, once or not at all</td></tr> <tr><td valign="top" headers="construct
 * greedy"><i>X</i><tt>*</tt></td> <td headers="matches"><i>X</i>, zero or more times</td></tr>
 * <tr><td valign="top" headers="construct greedy"><i>X</i><tt>+</tt></td> <td
 * headers="matches"><i>X</i>, one or more times</td></tr> <tr><td valign="top" headers="construct
 * greedy"><i>X</i><tt>{</tt><i>n</i><tt>}</tt></td> <td headers="matches"><i>X</i>, exactly
 * <i>n</i> times</td></tr> <tr><td valign="top" headers="construct greedy"><i>X</i><tt>{</tt><i>n</i><tt>,}</tt></td>
 * <td headers="matches"><i>X</i>, at least <i>n</i> times</td></tr> <tr><td valign="top"
 * headers="construct greedy"><i>X</i><tt>{</tt><i>n</i><tt>,</tt><i>m</i><tt>}</tt></td> <td
 * headers="matches"><i>X</i>, at least <i>n</i> but not more than <i>m</i> times</td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="reluc">Reluctant
 * quantifiers</th></tr>
 *
 * <tr><td valign="top" headers="construct reluc"><i>X</i><tt>??</tt></td> <td
 * headers="matches"><i>X</i>, once or not at all</td></tr> <tr><td valign="top" headers="construct
 * reluc"><i>X</i><tt>*?</tt></td> <td headers="matches"><i>X</i>, zero or more times</td></tr>
 * <tr><td valign="top" headers="construct reluc"><i>X</i><tt>+?</tt></td> <td
 * headers="matches"><i>X</i>, one or more times</td></tr> <tr><td valign="top" headers="construct
 * reluc"><i>X</i><tt>{</tt><i>n</i><tt>}?</tt></td> <td headers="matches"><i>X</i>, exactly
 * <i>n</i> times</td></tr> <tr><td valign="top" headers="construct reluc"><i>X</i><tt>{</tt><i>n</i><tt>,}?</tt></td>
 * <td headers="matches"><i>X</i>, at least <i>n</i> times</td></tr> <tr><td valign="top"
 * headers="construct reluc"><i>X</i><tt>{</tt><i>n</i><tt>,</tt><i>m</i><tt>}?</tt></td> <td
 * headers="matches"><i>X</i>, at least <i>n</i> but not more than <i>m</i> times</td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="poss">Possessive
 * quantifiers</th></tr>
 *
 * <tr><td valign="top" headers="construct poss"><i>X</i><tt>?+</tt></td> <td
 * headers="matches"><i>X</i>, once or not at all</td></tr> <tr><td valign="top" headers="construct
 * poss"><i>X</i><tt>*+</tt></td> <td headers="matches"><i>X</i>, zero or more times</td></tr>
 * <tr><td valign="top" headers="construct poss"><i>X</i><tt>++</tt></td> <td
 * headers="matches"><i>X</i>, one or more times</td></tr> <tr><td valign="top" headers="construct
 * poss"><i>X</i><tt>{</tt><i>n</i><tt>}+</tt></td> <td headers="matches"><i>X</i>, exactly <i>n</i>
 * times</td></tr> <tr><td valign="top" headers="construct poss"><i>X</i><tt>{</tt><i>n</i><tt>,}+</tt></td>
 * <td headers="matches"><i>X</i>, at least <i>n</i> times</td></tr> <tr><td valign="top"
 * headers="construct poss"><i>X</i><tt>{</tt><i>n</i><tt>,</tt><i>m</i><tt>}+</tt></td> <td
 * headers="matches"><i>X</i>, at least <i>n</i> but not more than <i>m</i> times</td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="logical">Logical
 * operators</th></tr>
 *
 * <tr><td valign="top" headers="construct logical"><i>XY</i></td> <td headers="matches"><i>X</i>
 * followed by <i>Y</i></td></tr> <tr><td valign="top" headers="construct
 * logical"><i>X</i><tt>|</tt><i>Y</i></td> <td headers="matches">Either <i>X</i> or
 * <i>Y</i></td></tr> <tr><td valign="top" headers="construct logical"><tt>(</tt><i>X</i><tt>)</tt></td>
 * <td headers="matches">X, as a <a href="#cg">capturing group</a></td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="backref">Back references</th></tr>
 *
 * <tr><td valign="bottom" headers="construct backref"><tt>\</tt><i>n</i></td> <td valign="bottom"
 * headers="matches">Whatever the <i>n</i><sup>th</sup> <a href="#cg">capturing group</a>
 * matched</td></tr>
 *
 * <tr><td valign="bottom" headers="construct backref"><tt>\</tt><i>k</i>&lt;<i>name</i>&gt;</td>
 * <td valign="bottom" headers="matches">Whatever the <a href="#groupname">named-capturing group</a>
 * "name" matched</td></tr>
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="quot">Quotation</th></tr>
 *
 * <tr><td valign="top" headers="construct quot"><tt>\</tt></td> <td headers="matches">Nothing, but
 * quotes the following character</td></tr> <tr><td valign="top" headers="construct
 * quot"><tt>\Q</tt></td> <td headers="matches">Nothing, but quotes all characters until
 * <tt>\E</tt></td></tr> <tr><td valign="top" headers="construct quot"><tt>\E</tt></td> <td
 * headers="matches">Nothing, but ends quoting started by <tt>\Q</tt></td></tr> <!-- Metachars:
 * !$()*+.<>?[\]^{|} -->
 *
 * <tr><th>&nbsp;</th></tr> <tr align="left"><th colspan="2" id="special">Special constructs
 * (named-capturing and non-capturing)</th></tr>
 *
 * <tr><td valign="top" headers="construct special"><tt>(?&lt;<a href="#groupname">name</a>&gt;</tt><i>X</i><tt>)</tt></td>
 * <td headers="matches"><i>X</i>, as a named-capturing group</td></tr> <tr><td valign="top"
 * headers="construct special"><tt>(?:</tt><i>X</i><tt>)</tt></td> <td headers="matches"><i>X</i>,
 * as a non-capturing group</td></tr> <tr><td valign="top" headers="construct
 * special"><tt>(?idmsuxU-idmsuxU)&nbsp;</tt></td> <td headers="matches">Nothing, but turns match
 * flags <a href="#CASE_INSENSITIVE">i</a> <a href="#UNIX_LINES">d</a> <a href="#MULTILINE">m</a> <a
 * href="#DOTALL">s</a> <a href="#UNICODE_CASE">u</a> <a href="#COMMENTS">x</a> <a
 * href="#UNICODE_CHARACTER_CLASS">U</a> on - off</td></tr> <tr><td valign="top" headers="construct
 * special"><tt>(?idmsux-idmsux:</tt><i>X</i><tt>)</tt>&nbsp;&nbsp;</td> <td
 * headers="matches"><i>X</i>, as a <a href="#cg">non-capturing group</a> with the given flags <a
 * href="#CASE_INSENSITIVE">i</a> <a href="#UNIX_LINES">d</a> <a href="#MULTILINE">m</a> <a
 * href="#DOTALL">s</a> <a href="#UNICODE_CASE">u</a > <a href="#COMMENTS">x</a> on - off</td></tr>
 * <tr><td valign="top" headers="construct special"><tt>(?=</tt><i>X</i><tt>)</tt></td> <td
 * headers="matches"><i>X</i>, via zero-width positive lookahead</td></tr> <tr><td valign="top"
 * headers="construct special"><tt>(?!</tt><i>X</i><tt>)</tt></td> <td headers="matches"><i>X</i>,
 * via zero-width negative lookahead</td></tr> <tr><td valign="top" headers="construct
 * special"><tt>(?&lt;=</tt><i>X</i><tt>)</tt></td> <td headers="matches"><i>X</i>, via zero-width
 * positive lookbehind</td></tr> <tr><td valign="top" headers="construct
 * special"><tt>(?&lt;!</tt><i>X</i><tt>)</tt></td> <td headers="matches"><i>X</i>, via zero-width
 * negative lookbehind</td></tr> <tr><td valign="top" headers="construct
 * special"><tt>(?&gt;</tt><i>X</i><tt>)</tt></td> <td headers="matches"><i>X</i>, as an
 * independent, non-capturing group</td></tr>
 *
 * </table>
 *
 * <hr>
 *
 *
 * <h3><a name="bs">Backslashes, escapes, and quoting</a></h3>
 *
 * <p> The backslash character (<tt>'\'</tt>) serves to introduce escaped constructs, as defined in
 * the table above, as well as to quote characters that otherwise would be interpreted as unescaped
 * constructs.  Thus the expression <tt>\\</tt> matches a single backslash and <tt>\{</tt> matches a
 * left brace.
 *
 * <p> It is an error to use a backslash prior to any alphabetic character that does not denote an
 * escaped construct; these are reserved for future extensions to the regular-expression language.
 * A backslash may be used prior to a non-alphabetic character regardless of whether that character
 * is part of an unescaped construct.
 *
 * <p> Backslashes within string literals in Java source code are interpreted as required by
 * <cite>The Java&trade; Language Specification</cite> as either Unicode escapes (section 3.3) or
 * other character escapes (section 3.10.6) It is therefore necessary to double backslashes in
 * string literals that represent regular expressions to protect them from interpretation by the
 * Java bytecode compiler.  The string literal <tt>"&#92;b"</tt>, for example, matches a single
 * backspace character when interpreted as a regular expression, while <tt>"&#92;&#92;b"</tt>
 * matches a word boundary.  The string literal <tt>"&#92;(hello&#92;)"</tt> is illegal and leads to
 * a compile-time error; in order to match the string <tt>(hello)</tt> the string literal
 * <tt>"&#92;&#92;(hello&#92;&#92;)"</tt> must be used.
 *
 * <h3><a name="cc">Character Classes</a></h3>
 *
 * <p> Character classes may appear within other character classes, and may be composed by the union
 * operator (implicit) and the intersection operator (<tt>&amp;&amp;</tt>). The union operator
 * denotes a class that contains every character that is in at least one of its operand classes.
 * The intersection operator denotes a class that contains every character that is in both of its
 * operand classes.
 *
 * <p> The precedence of character-class operators is as follows, from highest to lowest:
 *
 * <blockquote><table border="0" cellpadding="1" cellspacing="0" summary="Precedence of character
 * class operators."> <tr><th>1&nbsp;&nbsp;&nbsp;&nbsp;</th> <td>Literal
 * escape&nbsp;&nbsp;&nbsp;&nbsp;</td> <td><tt>\x</tt></td></tr> <tr><th>2&nbsp;&nbsp;&nbsp;&nbsp;</th>
 * <td>Grouping</td> <td><tt>[...]</tt></td></tr> <tr><th>3&nbsp;&nbsp;&nbsp;&nbsp;</th>
 * <td>Range</td> <td><tt>a-z</tt></td></tr> <tr><th>4&nbsp;&nbsp;&nbsp;&nbsp;</th> <td>Union</td>
 * <td><tt>[a-e][i-u]</tt></td></tr> <tr><th>5&nbsp;&nbsp;&nbsp;&nbsp;</th> <td>Intersection</td>
 * <td>{@code [a-z&&[aeiou]]}</td></tr> </table></blockquote>
 *
 * <p> Note that a different set of metacharacters are in effect inside a character class than
 * outside a character class. For instance, the regular expression <tt>.</tt> loses its special
 * meaning inside a character class, while the expression <tt>-</tt> becomes a range forming
 * metacharacter.
 *
 * <h3><a name="lt">Line terminators</a></h3>
 *
 * <p> A <i>line terminator</i> is a one- or two-character sequence that marks the end of a line of
 * the input character sequence.  The following are recognized as line terminators:
 *
 * <ul>
 *
 * <li> A newline (line feed) character&nbsp;(<tt>'\n'</tt>),
 *
 * <li> A carriage-return character followed immediately by a newline
 * character&nbsp;(<tt>"\r\n"</tt>),
 *
 * <li> A standalone carriage-return character&nbsp;(<tt>'\r'</tt>),
 *
 * <li> A next-line character&nbsp;(<tt>'&#92;u0085'</tt>),
 *
 * <li> A line-separator character&nbsp;(<tt>'&#92;u2028'</tt>), or
 *
 * <li> A paragraph-separator character&nbsp;(<tt>'&#92;u2029</tt>).
 *
 * </ul> <p>If {@link #UNIX_LINES} mode is activated, then the only line terminators recognized are
 * newline characters.
 *
 * <p> The regular expression <tt>.</tt> matches any character except a line terminator unless the
 * {@link #DOTALL} flag is specified.
 *
 * <p> By default, the regular expressions <tt>^</tt> and <tt>$</tt> ignore line terminators and
 * only match at the beginning and the end, respectively, of the entire input sequence. If {@link
 * #MULTILINE} mode is activated then <tt>^</tt> matches at the beginning of input and after any
 * line terminator except at the end of input. When in {@link #MULTILINE} mode <tt>$</tt> matches
 * just before a line terminator or the end of the input sequence.
 *
 * <h3><a name="cg">Groups and capturing</a></h3>
 *
 * <h4><a name="gnumber">Group number</a></h4> <p> Capturing groups are numbered by counting their
 * opening parentheses from left to right.  In the expression <tt>((A)(B(C)))</tt>, for example,
 * there are four such groups: </p>
 *
 * <blockquote><table cellpadding=1 cellspacing=0 summary="Capturing group numberings">
 * <tr><th>1&nbsp;&nbsp;&nbsp;&nbsp;</th> <td><tt>((A)(B(C)))</tt></td></tr>
 * <tr><th>2&nbsp;&nbsp;&nbsp;&nbsp;</th> <td><tt>(A)</tt></td></tr>
 * <tr><th>3&nbsp;&nbsp;&nbsp;&nbsp;</th> <td><tt>(B(C))</tt></td></tr>
 * <tr><th>4&nbsp;&nbsp;&nbsp;&nbsp;</th> <td><tt>(C)</tt></td></tr> </table></blockquote>
 *
 * <p> Group zero always stands for the entire expression.
 *
 * <p> Capturing groups are so named because, during a match, each subsequence of the input sequence
 * that matches such a group is saved.  The captured subsequence may be used later in the
 * expression, via a back reference, and may also be retrieved from the matcher once the match
 * operation is complete.
 *
 * <h4><a name="groupname">Group name</a></h4> <p>A capturing group can also be assigned a "name", a
 * <tt>named-capturing group</tt>, and then be back-referenced later by the "name". Group names are
 * composed of the following characters. The first character must be a <tt>letter</tt>.
 *
 * <ul> <li> The uppercase letters <tt>'A'</tt> through <tt>'Z'</tt>
 * (<tt>'&#92;u0041'</tt>&nbsp;through&nbsp;<tt>'&#92;u005a'</tt>), <li> The lowercase letters
 * <tt>'a'</tt> through <tt>'z'</tt> (<tt>'&#92;u0061'</tt>&nbsp;through&nbsp;<tt>'&#92;u007a'</tt>),
 * <li> The digits <tt>'0'</tt> through <tt>'9'</tt> (<tt>'&#92;u0030'</tt>&nbsp;through&nbsp;<tt>'&#92;u0039'</tt>),
 * </ul>
 *
 * <p> A <tt>named-capturing group</tt> is still numbered as described in <a href="#gnumber">Group
 * number</a>.
 *
 * <p> The captured input associated with a group is always the subsequence that the group most
 * recently matched.  If a group is evaluated a second time because of quantification then its
 * previously-captured value, if any, will be retained if the second evaluation fails.  Matching the
 * string <tt>"aba"</tt> against the expression <tt>(a(b)?)+</tt>, for example, leaves group two set
 * to <tt>"b"</tt>.  All captured input is discarded at the beginning of each match.
 *
 * <p> Groups beginning with <tt>(?</tt> are either pure, <i>non-capturing</i> groups that do not
 * capture text and do not count towards the group total, or <i>named-capturing</i> group.
 *
 * <h3> Unicode support </h3>
 *
 * <p> This class is in conformance with Level 1 of <a href="http://www.unicode.org/reports/tr18/"><i>Unicode
 * Technical Standard #18: Unicode Regular Expression</i></a>, plus RL2.1 Canonical Equivalents. <p>
 * <b>Unicode escape sequences</b> such as <tt>&#92;u2014</tt> in Java source code are processed as
 * described in section 3.3 of <cite>The Java&trade; Language Specification</cite>. Such escape
 * sequences are also implemented directly by the regular-expression parser so that Unicode escapes
 * can be used in expressions that are read from files or from the keyboard.  Thus the strings
 * <tt>"&#92;u2014"</tt> and <tt>"\\u2014"</tt>, while not equal, compile into the same pattern,
 * which matches the character with hexadecimal value <tt>0x2014</tt>. <p> A Unicode character can
 * also be represented in a regular-expression by using its <b>Hex notation</b>(hexadecimal code
 * point value) directly as described in construct <tt>&#92;x{...}</tt>, for example a supplementary
 * character U+2011F can be specified as <tt>&#92;x{2011F}</tt>, instead of two consecutive Unicode
 * escape sequences of the surrogate pair <tt>&#92;uD840</tt><tt>&#92;uDD1F</tt>. <p> Unicode
 * scripts, blocks, categories and binary properties are written with the <tt>\p</tt> and
 * <tt>\P</tt> constructs as in Perl. <tt>\p{</tt><i>prop</i><tt>}</tt> matches if the input has the
 * property <i>prop</i>, while <tt>\P{</tt><i>prop</i><tt>}</tt> does not match if the input has
 * that property. <p> Scripts, blocks, categories and binary properties can be used both inside and
 * outside of a character class.
 *
 * <p> <b><a name="usc">Scripts</a></b> are specified either with the prefix {@code Is}, as in
 * {@code IsHiragana}, or by using  the {@code script} keyword (or its short form {@code sc})as in
 * {@code script=Hiragana} or {@code sc=Hiragana}. <p> The script names supported by
 * <code>Pattern</code> are the valid script names accepted and defined by {@link
 * java.lang.Character.UnicodeScript#forName(String) UnicodeScript.forName}.
 *
 * <p> <b><a name="ubc">Blocks</a></b> are specified with the prefix {@code In}, as in {@code
 * InMongolian}, or by using the keyword {@code block} (or its short form {@code blk}) as in {@code
 * block=Mongolian} or {@code blk=Mongolian}. <p> The block names supported by <code>Pattern</code>
 * are the valid block names accepted and defined by {@link java.lang.Character.UnicodeBlock#forName(String)
 * UnicodeBlock.forName}. <p>
 *
 * <b><a name="ucc">Categories</a></b> may be specified with the optional prefix {@code Is}: Both
 * {@code \p{L}} and {@code \p{IsL}} denote the category of Unicode letters. Same as scripts and
 * blocks, categories can also be specified by using the keyword {@code general_category} (or its
 * short form {@code gc}) as in {@code general_category=Lu} or {@code gc=Lu}. <p> The supported
 * categories are those of <a href="http://www.unicode.org/unicode/standard/standard.html"> <i>The
 * Unicode Standard</i></a> in the version specified by the {@link java.lang.Character Character}
 * class. The category names are those defined in the Standard, both normative and informative. <p>
 *
 * <b><a name="ubpc">Binary properties</a></b> are specified with the prefix {@code Is}, as in
 * {@code IsAlphabetic}. The supported binary properties by <code>Pattern</code> are <ul> <li>
 * Alphabetic <li> Ideographic <li> Letter <li> Lowercase <li> Uppercase <li> Titlecase <li>
 * Punctuation <Li> Control <li> White_Space <li> Digit <li> Hex_Digit <li> Join_Control <li>
 * Noncharacter_Code_Point <li> Assigned </ul> <p> The following <b>Predefined Character classes</b>
 * and <b>POSIX character classes</b> are in conformance with the recommendation of <i>Annex C:
 * Compatibility Properties</i> of <a href="http://www.unicode.org/reports/tr18/"><i>Unicode Regular
 * Expression </i></a>, when {@link #UNICODE_CHARACTER_CLASS} flag is specified.
 *
 * <table border="0" cellpadding="1" cellspacing="0" summary="predefined and posix character classes
 * in Unicode mode"> <tr align="left"> <th align="left" id="predef_classes">Classes</th> <th
 * align="left" id="predef_matches">Matches</th> </tr> <tr><td><tt>\p{Lower}</tt></td> <td>A
 * lowercase character:<tt>\p{IsLowercase}</tt></td></tr> <tr><td><tt>\p{Upper}</tt></td> <td>An
 * uppercase character:<tt>\p{IsUppercase}</tt></td></tr> <tr><td><tt>\p{ASCII}</tt></td> <td>All
 * ASCII:<tt>[\x00-\x7F]</tt></td></tr> <tr><td><tt>\p{Alpha}</tt></td> <td>An alphabetic
 * character:<tt>\p{IsAlphabetic}</tt></td></tr> <tr><td><tt>\p{Digit}</tt></td> <td>A decimal digit
 * character:<tt>p{IsDigit}</tt></td></tr> <tr><td><tt>\p{Alnum}</tt></td> <td>An alphanumeric
 * character:<tt>[\p{IsAlphabetic}\p{IsDigit}]</tt></td></tr> <tr><td><tt>\p{Punct}</tt></td> <td>A
 * punctuation character:<tt>p{IsPunctuation}</tt></td></tr> <tr><td><tt>\p{Graph}</tt></td> <td>A
 * visible character: <tt>[^\p{IsWhite_Space}\p{gc=Cc}\p{gc=Cs}\p{gc=Cn}]</tt></td></tr>
 * <tr><td><tt>\p{Print}</tt></td> <td>A printable character: {@code
 * [\p{Graph}\p{Blank}&&[^\p{Cntrl}]]}</td></tr> <tr><td><tt>\p{Blank}</tt></td> <td>A space or a
 * tab: {@code [\p{IsWhite_Space}&&[^\p{gc=Zl}\p{gc=Zp}\x0a\x0b\x0c\x0d\x85]]}</td></tr>
 * <tr><td><tt>\p{Cntrl}</tt></td> <td>A control character: <tt>\p{gc=Cc}</tt></td></tr>
 * <tr><td><tt>\p{XDigit}</tt></td> <td>A hexadecimal digit: <tt>[\p{gc=Nd}\p{IsHex_Digit}]</tt></td></tr>
 * <tr><td><tt>\p{Space}</tt></td> <td>A whitespace character:<tt>\p{IsWhite_Space}</tt></td></tr>
 * <tr><td><tt>\d</tt></td> <td>A digit: <tt>\p{IsDigit}</tt></td></tr> <tr><td><tt>\D</tt></td>
 * <td>A non-digit: <tt>[^\d]</tt></td></tr> <tr><td><tt>\s</tt></td> <td>A whitespace character:
 * <tt>\p{IsWhite_Space}</tt></td></tr> <tr><td><tt>\S</tt></td> <td>A non-whitespace character:
 * <tt>[^\s]</tt></td></tr> <tr><td><tt>\w</tt></td> <td>A word character:
 * <tt>[\p{Alpha}\p{gc=Mn}\p{gc=Me}\p{gc=Mc}\p{Digit}\p{gc=Pc}\p{IsJoin_Control}]</tt></td></tr>
 * <tr><td><tt>\W</tt></td> <td>A non-word character: <tt>[^\w]</tt></td></tr> </table> <p> <a
 * name="jcc"> Categories that behave like the java.lang.Character boolean is<i>methodname</i>
 * methods (except for the deprecated ones) are available through the same
 * <tt>\p{</tt><i>prop</i><tt>}</tt> syntax where the specified property has the name
 * <tt>java<i>methodname</i></tt></a>.
 *
 * <h3> Comparison to Perl 5 </h3>
 *
 * <p>The <code>Pattern</code> engine performs traditional NFA-based matching with ordered
 * alternation as occurs in Perl 5.
 *
 * <p> Perl constructs not supported by this class: </p>
 *
 * <ul> <li><p> Predefined character classes (Unicode character) <p><tt>\X&nbsp;&nbsp;&nbsp;&nbsp;</tt>Match
 * Unicode <a href="http://www.unicode.org/reports/tr18/#Default_Grapheme_Clusters"> <i>extended
 * grapheme cluster</i></a> </p></li>
 *
 * <li><p> The backreference constructs, <tt>\g{</tt><i>n</i><tt>}</tt> for the
 * <i>n</i><sup>th</sup><a href="#cg">capturing group</a> and <tt>\g{</tt><i>name</i><tt>}</tt> for
 * <a href="#groupname">named-capturing group</a>. </p></li>
 *
 * <li><p> The named character construct, <tt>\N{</tt><i>name</i><tt>}</tt> for a Unicode character
 * by its name. </p></li>
 *
 * <li><p> The conditional constructs <tt>(?(</tt><i>condition</i><tt>)</tt><i>X</i><tt>)</tt> and
 * <tt>(?(</tt><i>condition</i><tt>)</tt><i>X</i><tt>|</tt><i>Y</i><tt>)</tt>, </p></li>
 *
 * <li><p> The embedded code constructs <tt>(?{</tt><i>code</i><tt>})</tt> and
 * <tt>(??{</tt><i>code</i><tt>})</tt>,</p></li>
 *
 * <li><p> The embedded comment syntax <tt>(?#comment)</tt>, and </p></li>
 *
 * <li><p> The preprocessing operations <tt>\l</tt> <tt>&#92;u</tt>, <tt>\L</tt>, and <tt>\U</tt>.
 * </p></li>
 *
 * </ul>
 *
 * <p> Constructs supported by this class but not by Perl: </p>
 *
 * <ul>
 *
 * <li><p> Character-class union and intersection as described <a href="#cc">above</a>.</p></li>
 *
 * </ul>
 *
 * <p> Notable differences from Perl: </p>
 *
 * <ul>
 *
 * <li><p> In Perl, <tt>\1</tt> through <tt>\9</tt> are always interpreted as back references; a
 * backslash-escaped number greater than <tt>9</tt> is treated as a back reference if at least that
 * many subexpressions exist, otherwise it is interpreted, if possible, as an octal escape.  In this
 * class octal escapes must always begin with a zero. In this class, <tt>\1</tt> through <tt>\9</tt>
 * are always interpreted as back references, and a larger number is accepted as a back reference if
 * at least that many subexpressions exist at that point in the regular expression, otherwise the
 * parser will drop digits until the number is smaller or equal to the existing number of groups or
 * it is one digit. </p></li>
 *
 * <li><p> Perl uses the <tt>g</tt> flag to request a match that resumes where the last match left
 * off.  This functionality is provided implicitly by the {@link Matcher} class: Repeated
 * invocations of the {@link Matcher#find find} method will resume where the last match left off,
 * unless the matcher is reset.  </p></li>
 *
 * <li><p> In Perl, embedded flags at the top level of an expression affect the whole expression.
 * In this class, embedded flags always take effect at the point at which they appear, whether they
 * are at the top level or within a group; in the latter case, flags are restored at the end of the
 * group just as in Perl.  </p></li>
 *
 * </ul>
 *
 *
 * <p> For a more precise description of the behavior of regular expression constructs, please see
 * <a href="http://www.oreilly.com/catalog/regex3/"> <i>Mastering Regular Expressions, 3nd
 * Edition</i>, Jeffrey E. F. Friedl, O'Reilly and Associates, 2006.</a> </p>
 *
 * @author Mike McCloskey
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @spec JSR-51
 * @see java.lang.String#split(String, int)
 * @see java.lang.String#split(String)
 * @since 1.4
 */

public final class Pattern
    implements java.io.Serializable {

  /**
   * Regular expression modifier values.  Instead of being passed as
   * arguments, they can also be passed as inline modifiers.
   * For example, the following statements have the same effect.
   * <pre>
   * RegExp r1 = RegExp.compile("abc", Pattern.I|Pattern.M);
   * RegExp r2 = RegExp.compile("(?im)abc", 0);
   * </pre>
   *
   * The flags are duplicated so that the familiar Perl match flag
   * names are available.
   */

  /**
   * Enables Unix lines mode.
   *
   * <p> In this mode, only the <tt>'\n'</tt> line terminator is recognized
   * in the behavior of <tt>.</tt>, <tt>^</tt>, and <tt>$</tt>.
   *
   * <p> Unix lines mode can also be enabled via the embedded flag
   * expression&nbsp;<tt>(?d)</tt>.
   */
  public static final int UNIX_LINES = 0x01;

  /**
   * Enables case-insensitive matching.
   *
   * <p> By default, case-insensitive matching assumes that only characters
   * in the US-ASCII charset are being matched.  Unicode-aware
   * case-insensitive matching can be enabled by specifying the {@link
   * #UNICODE_CASE} flag in conjunction with this flag.
   *
   * <p> Case-insensitive matching can also be enabled via the embedded flag
   * expression&nbsp;<tt>(?i)</tt>.
   *
   * <p> Specifying this flag may impose a slight performance penalty.  </p>
   */
  public static final int CASE_INSENSITIVE = 0x02;

  /**
   * Permits whitespace and comments in pattern.
   *
   * <p> In this mode, whitespace is ignored, and embedded comments starting
   * with <tt>#</tt> are ignored until the end of a line.
   *
   * <p> Comments mode can also be enabled via the embedded flag
   * expression&nbsp;<tt>(?x)</tt>.
   */
  public static final int COMMENTS = 0x04;

  /**
   * Enables multiline mode.
   *
   * <p> In multiline mode the expressions <tt>^</tt> and <tt>$</tt> match
   * just after or just before, respectively, a line terminator or the end of
   * the input sequence.  By default these expressions only match at the
   * beginning and the end of the entire input sequence.
   *
   * <p> Multiline mode can also be enabled via the embedded flag
   * expression&nbsp;<tt>(?m)</tt>.  </p>
   */
  public static final int MULTILINE = 0x08;

  /**
   * Enables literal parsing of the pattern.
   *
   * <p> When this flag is specified then the input string that specifies
   * the pattern is treated as a sequence of literal characters.
   * Metacharacters or escape sequences in the input sequence will be
   * given no special meaning.
   *
   * <p>The flags CASE_INSENSITIVE and UNICODE_CASE retain their impact on
   * matching when used in conjunction with this flag. The other flags
   * become superfluous.
   *
   * <p> There is no embedded flag character for enabling literal parsing.
   *
   * @since 1.5
   */
  public static final int LITERAL = 0x10;

  /**
   * Enables dotall mode.
   *
   * <p> In dotall mode, the expression <tt>.</tt> matches any character,
   * including a line terminator.  By default this expression does not match
   * line terminators.
   *
   * <p> Dotall mode can also be enabled via the embedded flag
   * expression&nbsp;<tt>(?s)</tt>.  (The <tt>s</tt> is a mnemonic for
   * "single-line" mode, which is what this is called in Perl.)  </p>
   */
  public static final int DOTALL = 0x20;

  /**
   * Enables Unicode-aware case folding.
   *
   * <p> When this flag is specified then case-insensitive matching, when
   * enabled by the {@link #CASE_INSENSITIVE} flag, is done in a manner
   * consistent with the Unicode Standard.  By default, case-insensitive
   * matching assumes that only characters in the US-ASCII charset are being
   * matched.
   *
   * <p> Unicode-aware case folding can also be enabled via the embedded flag
   * expression&nbsp;<tt>(?u)</tt>.
   *
   * <p> Specifying this flag may impose a performance penalty.  </p>
   */
  public static final int UNICODE_CASE = 0x40;

  /**
   * Enables canonical equivalence.
   *
   * <p> When this flag is specified then two characters will be considered
   * to match if, and only if, their full canonical decompositions match.
   * The expression <tt>"a&#92;u030A"</tt>, for example, will match the
   * string <tt>"&#92;u00E5"</tt> when this flag is specified.  By default,
   * matching does not take canonical equivalence into account.
   *
   * <p> There is no embedded flag character for enabling canonical
   * equivalence.
   *
   * <p> Specifying this flag may impose a performance penalty.  </p>
   */
  public static final int CANON_EQ = 0x80;

  /**
   * Enables the Unicode version of <i>Predefined character classes</i> and
   * <i>POSIX character classes</i>.
   *
   * <p> When this flag is specified then the (US-ASCII only)
   * <i>Predefined character classes</i> and <i>POSIX character classes</i>
   * are in conformance with
   * <a href="http://www.unicode.org/reports/tr18/"><i>Unicode Technical
   * Standard #18: Unicode Regular Expression</i></a>
   * <i>Annex C: Compatibility Properties</i>.
   * <p>
   * The UNICODE_CHARACTER_CLASS mode can also be enabled via the embedded
   * flag expression&nbsp;<tt>(?U)</tt>.
   * <p>
   * The flag implies UNICODE_CASE, that is, it enables Unicode-aware case
   * folding.
   * <p>
   * Specifying this flag may impose a performance penalty.  </p>
   *
   * @since 1.7
   */
  public static final int UNICODE_CHARACTER_CLASS = 0x100;

    /* Pattern has only two serialized components: The pattern string
     * and the flags, which are all that is needed to recompile the pattern
     * when it is deserialized.
     */

  /**
   * use serialVersionUID from Merlin b59 for interoperability
   */
  private static final long serialVersionUID = 5073258162644648461L;

  /**
   * The original regular-expression pattern string.
   *
   * @serial
   */
  private String pattern;

  /**
   * The original pattern flags.
   *
   * @serial
   */
  private int flags;

  /**
   * Boolean indicating this Pattern is compiled; this is necessary in order
   * to lazily compile deserialized Patterns.
   */
  private transient volatile boolean compiled = false;

  /**
   * The normalized pattern string.
   */
  private transient String normalizedPattern;

  /**
   * The starting point of state machine for the find operation.  This allows
   * a match to start anywhere in the input.
   */
  transient Node root;

  /**
   * The root of object tree for a match operation.  The pattern is matched
   * at the beginning.  This may include a find that uses BnM or a First
   * node.
   */
  transient Node matchRoot;

  /**
   * Temporary storage used by parsing pattern slice.
   */
  transient int[] buffer;

  /**
   * Map the "name" of the "named capturing group" to its group id
   * node.
   */
  transient volatile Map<String, Integer> namedGroups;

  /**
   * Temporary storage used while parsing group references.
   */
  transient GroupHead[] groupNodes;

  /**
   * Temporary null terminated code point array used by pattern compiling.
   */
  private transient int[] temp;

  /**
   * The number of capturing groups in this Pattern. Used by matchers to
   * allocate storage needed to perform a match.
   */
  transient int capturingGroupCount;

  /**
   * The local variable count used by parsing tree. Used by matchers to
   * allocate storage needed to perform a match.
   */
  transient int localCount;

  /**
   * Index into the pattern string that keeps track of how much has been
   * parsed.
   */
  private transient int cursor;

  /**
   * Holds the length of the pattern string.
   */
  private transient int patternLength;

  /**
   * If the Start node might possibly match supplementary characters.
   * It is set to true during compiling if
   * (1) There is supplementary char in pattern, or
   * (2) There is complement node of Category or Block
   */
  private transient boolean hasSupplementary;

  /**
   * Compiles the given regular expression into a pattern.
   *
   * @param regex The expression to be compiled
   * @return the given regular expression compiled into a pattern
   * @throws PatternSyntaxException If the expression's syntax is invalid
   */
  public static Pattern compile(String regex) {
    return new Pattern(regex, 0);
  }

  /**
   * Compiles the given regular expression into a pattern with the given
   * flags.
   *
   * @param regex The expression to be compiled
   * @param flags Match flags, a bit mask that may include {@link #CASE_INSENSITIVE}, {@link
   * #MULTILINE}, {@link #DOTALL}, {@link #UNICODE_CASE}, {@link #CANON_EQ}, {@link #UNIX_LINES},
   * {@link #LITERAL}, {@link #UNICODE_CHARACTER_CLASS} and {@link #COMMENTS}
   * @return the given regular expression compiled into a pattern with the given flags
   * @throws IllegalArgumentException If bit values other than those corresponding to the defined
   * match flags are set in <tt>flags</tt>
   * @throws PatternSyntaxException If the expression's syntax is invalid
   */
  public static Pattern compile(String regex, int flags) {
    return new Pattern(regex, flags);
  }

  /**
   * Returns the regular expression from which this pattern was compiled.
   *
   * @return The source of this pattern
   */
  public String pattern() {
    return pattern;
  }

  /**
   * <p>Returns the string representation of this pattern. This
   * is the regular expression from which this pattern was
   * compiled.</p>
   *
   * @return The string representation of this pattern
   * @since 1.5
   */
  public String toString() {
    return pattern;
  }

  /**
   * Creates a matcher that will match the given input against this pattern.
   *
   * @param input The character sequence to be matched
   * @return A new matcher for this pattern
   */
  public Matcher matcher(CharSequence input) {
    if (!compiled) {
      synchronized (this) {
        if (!compiled) {
          compile();
        }
      }
    }
    Matcher m = new Matcher(this, input);
    return m;
  }

  /**
   * Returns this pattern's match flags.
   *
   * @return The match flags specified when this pattern was compiled
   */
  public int flags() {
    return flags;
  }

  /**
   * Compiles the given regular expression and attempts to match the given
   * input against it.
   *
   * <p> An invocation of this convenience method of the form
   *
   * <blockquote><pre>
   * Pattern.matches(regex, input);</pre></blockquote>
   *
   * behaves in exactly the same way as the expression
   *
   * <blockquote><pre>
   * Pattern.compile(regex).matcher(input).matches()</pre></blockquote>
   *
   * <p> If a pattern is to be used multiple times, compiling it once and reusing
   * it will be more efficient than invoking this method each time.  </p>
   *
   * @param regex The expression to be compiled
   * @param input The character sequence to be matched
   * @return whether or not the regular expression matches on the input
   * @throws PatternSyntaxException If the expression's syntax is invalid
   */
  public static boolean matches(String regex, CharSequence input) {
    Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(input);
    return m.matches();
  }

  /**
   * Splits the given input sequence around matches of this pattern.
   *
   * <p> The array returned by this method contains each substring of the
   * input sequence that is terminated by another subsequence that matches
   * this pattern or is terminated by the end of the input sequence.  The
   * substrings in the array are in the order in which they occur in the
   * input. If this pattern does not match any subsequence of the input then
   * the resulting array has just one element, namely the input sequence in
   * string form.
   *
   * <p> When there is a positive-width match at the beginning of the input
   * sequence then an empty leading substring is included at the beginning
   * of the resulting array. A zero-width match at the beginning however
   * never produces such empty leading substring.
   *
   * <p> The <tt>limit</tt> parameter controls the number of times the
   * pattern is applied and therefore affects the length of the resulting
   * array.  If the limit <i>n</i> is greater than zero then the pattern
   * will be applied at most <i>n</i>&nbsp;-&nbsp;1 times, the array's
   * length will be no greater than <i>n</i>, and the array's last entry
   * will contain all input beyond the last matched delimiter.  If <i>n</i>
   * is non-positive then the pattern will be applied as many times as
   * possible and the array can have any length.  If <i>n</i> is zero then
   * the pattern will be applied as many times as possible, the array can
   * have any length, and trailing empty strings will be discarded.
   *
   * <p> The input <tt>"boo:and:foo"</tt>, for example, yields the following
   * results with these parameters:
   *
   * <blockquote><table cellpadding=1 cellspacing=0
   * summary="Split examples showing regex, limit, and result">
   * <tr><th align="left"><i>Regex&nbsp;&nbsp;&nbsp;&nbsp;</i></th>
   * <th align="left"><i>Limit&nbsp;&nbsp;&nbsp;&nbsp;</i></th>
   * <th align="left"><i>Result&nbsp;&nbsp;&nbsp;&nbsp;</i></th></tr>
   * <tr><td align=center>:</td>
   * <td align=center>2</td>
   * <td><tt>{ "boo", "and:foo" }</tt></td></tr>
   * <tr><td align=center>:</td>
   * <td align=center>5</td>
   * <td><tt>{ "boo", "and", "foo" }</tt></td></tr>
   * <tr><td align=center>:</td>
   * <td align=center>-2</td>
   * <td><tt>{ "boo", "and", "foo" }</tt></td></tr>
   * <tr><td align=center>o</td>
   * <td align=center>5</td>
   * <td><tt>{ "b", "", ":and:f", "", "" }</tt></td></tr>
   * <tr><td align=center>o</td>
   * <td align=center>-2</td>
   * <td><tt>{ "b", "", ":and:f", "", "" }</tt></td></tr>
   * <tr><td align=center>o</td>
   * <td align=center>0</td>
   * <td><tt>{ "b", "", ":and:f" }</tt></td></tr>
   * </table></blockquote>
   *
   * @param input The character sequence to be split
   * @param limit The result threshold, as described above
   * @return The array of strings computed by splitting the input around matches of this pattern
   */
  public String[] split(CharSequence input, int limit) {
    int index = 0;
    boolean matchLimited = limit > 0;
    ArrayList<String> matchList = new ArrayList<>();
    Matcher m = matcher(input);

    // Add segments before each match found
    while (m.find()) {
      if (!matchLimited || matchList.size() < limit - 1) {
        if (index == 0 && index == m.start() && m.start() == m.end()) {
          // no empty leading substring included for zero-width match
          // at the beginning of the input char sequence.
          continue;
        }
        String match = input.subSequence(index, m.start()).toString();
        matchList.add(match);
        index = m.end();
      } else if (matchList.size() == limit - 1) { // last one
        String match = input.subSequence(index,
            input.length()).toString();
        matchList.add(match);
        index = m.end();
      }
    }

    // If no match was found, return this
    if (index == 0) {
      return new String[]{input.toString()};
    }

    // Add remaining segment
    if (!matchLimited || matchList.size() < limit) {
      matchList.add(input.subSequence(index, input.length()).toString());
    }

    // Construct result
    int resultSize = matchList.size();
    if (limit == 0) {
      while (resultSize > 0 && matchList.get(resultSize - 1).equals("")) {
        resultSize--;
      }
    }
    String[] result = new String[resultSize];
    return matchList.subList(0, resultSize).toArray(result);
  }

  /**
   * Splits the given input sequence around matches of this pattern.
   *
   * <p> This method works as if by invoking the two-argument {@link
   * #split(java.lang.CharSequence, int) split} method with the given input
   * sequence and a limit argument of zero.  Trailing empty strings are
   * therefore not included in the resulting array. </p>
   *
   * <p> The input <tt>"boo:and:foo"</tt>, for example, yields the following
   * results with these expressions:
   *
   * <blockquote><table cellpadding=1 cellspacing=0
   * summary="Split examples showing regex and result">
   * <tr><th align="left"><i>Regex&nbsp;&nbsp;&nbsp;&nbsp;</i></th>
   * <th align="left"><i>Result</i></th></tr>
   * <tr><td align=center>:</td>
   * <td><tt>{ "boo", "and", "foo" }</tt></td></tr>
   * <tr><td align=center>o</td>
   * <td><tt>{ "b", "", ":and:f" }</tt></td></tr>
   * </table></blockquote>
   *
   * @param input The character sequence to be split
   * @return The array of strings computed by splitting the input around matches of this pattern
   */
  public String[] split(CharSequence input) {
    return split(input, 0);
  }

  /**
   * Returns a literal pattern <code>String</code> for the specified
   * <code>String</code>.
   *
   * <p>This method produces a <code>String</code> that can be used to
   * create a <code>Pattern</code> that would match the string
   * <code>s</code> as if it were a literal pattern.</p> Metacharacters
   * or escape sequences in the input sequence will be given no special
   * meaning.
   *
   * @param s The string to be literalized
   * @return A literal string replacement
   * @since 1.5
   */
  public static String quote(String s) {
    int slashEIndex = s.indexOf("\\E");
    if (slashEIndex == -1) {
      return "\\Q" + s + "\\E";
    }

    StringBuilder sb = new StringBuilder(s.length() * 2);
    sb.append("\\Q");
    slashEIndex = 0;
    int current = 0;
    while ((slashEIndex = s.indexOf("\\E", current)) != -1) {
      sb.append(s.substring(current, slashEIndex));
      current = slashEIndex + 2;
      sb.append("\\E\\\\E\\Q");
    }
    sb.append(s.substring(current, s.length()));
    sb.append("\\E");
    return sb.toString();
  }

  /**
   * Recompile the Pattern instance from a stream.  The original pattern
   * string is read in and the object tree is recompiled from it.
   */
  private void readObject(java.io.ObjectInputStream s)
      throws java.io.IOException, ClassNotFoundException {

    // Read in all fields
    s.defaultReadObject();

    // Initialize counts
    capturingGroupCount = 1;
    localCount = 0;

    // if length > 0, the Pattern is lazily compiled
    compiled = false;
    if (pattern.length() == 0) {
      root = new Start(lastAccept);
      matchRoot = lastAccept;
      compiled = true;
    }
  }

  /**
   * This private constructor is used to create all Patterns. The pattern
   * string and match flags are all that is needed to completely describe
   * a Pattern. An empty pattern string results in an object tree with
   * only a Start node and a LastNode node.
   */
  private Pattern(String p, int f) {
    pattern = p;
    flags = f;

    // to use UNICODE_CASE if UNICODE_CHARACTER_CLASS present
    if ((flags & UNICODE_CHARACTER_CLASS) != 0) {
      flags |= UNICODE_CASE;
    }

    // Reset group index count
    capturingGroupCount = 1;
    localCount = 0;

    if (pattern.length() > 0) {
      compile();
    } else {
      root = new Start(lastAccept);
      matchRoot = lastAccept;
    }
  }

  /**
   * The pattern is converted to normalizedD form and then a pure group
   * is constructed to match canonical equivalences of the characters.
   */
  private void normalize() {
    boolean inCharClass = false;
    int lastCodePoint = -1;

    // Convert pattern into normalizedD form
    normalizedPattern = Normalizer.normalize(pattern, Normalizer.Form.NFD);
    patternLength = normalizedPattern.length();

    // Modify pattern to match canonical equivalences
    StringBuilder newPattern = new StringBuilder(patternLength);
    for (int i = 0; i < patternLength; ) {
      int c = normalizedPattern.codePointAt(i);
      StringBuilder sequenceBuffer;
      if ((Character.getType(c) == Character.NON_SPACING_MARK)
          && (lastCodePoint != -1)) {
        sequenceBuffer = new StringBuilder();
        sequenceBuffer.appendCodePoint(lastCodePoint);
        sequenceBuffer.appendCodePoint(c);
        while (Character.getType(c) == Character.NON_SPACING_MARK) {
          i += Character.charCount(c);
          if (i >= patternLength) {
            break;
          }
          c = normalizedPattern.codePointAt(i);
          sequenceBuffer.appendCodePoint(c);
        }
        String ea = produceEquivalentAlternation(
            sequenceBuffer.toString());
        newPattern.setLength(newPattern.length() - Character.charCount(lastCodePoint));
        newPattern.append("(?:").append(ea).append(")");
      } else if (c == '[' && lastCodePoint != '\\') {
        i = normalizeCharClass(newPattern, i);
      } else {
        newPattern.appendCodePoint(c);
      }
      lastCodePoint = c;
      i += Character.charCount(c);
    }
    normalizedPattern = newPattern.toString();
  }

  /**
   * Complete the character class being parsed and add a set
   * of alternations to it that will match the canonical equivalences
   * of the characters within the class.
   */
  private int normalizeCharClass(StringBuilder newPattern, int i) {
    StringBuilder charClass = new StringBuilder();
    StringBuilder eq = null;
    int lastCodePoint = -1;
    String result;

    i++;
    charClass.append("[");
    while (true) {
      int c = normalizedPattern.codePointAt(i);
      StringBuilder sequenceBuffer;

      if (c == ']' && lastCodePoint != '\\') {
        charClass.append((char) c);
        break;
      } else if (Character.getType(c) == Character.NON_SPACING_MARK) {
        sequenceBuffer = new StringBuilder();
        sequenceBuffer.appendCodePoint(lastCodePoint);
        while (Character.getType(c) == Character.NON_SPACING_MARK) {
          sequenceBuffer.appendCodePoint(c);
          i += Character.charCount(c);
          if (i >= normalizedPattern.length()) {
            break;
          }
          c = normalizedPattern.codePointAt(i);
        }
        String ea = produceEquivalentAlternation(
            sequenceBuffer.toString());

        charClass.setLength(charClass.length() - Character.charCount(lastCodePoint));
        if (eq == null) {
          eq = new StringBuilder();
        }
        eq.append('|');
        eq.append(ea);
      } else {
        charClass.appendCodePoint(c);
        i++;
      }
      if (i == normalizedPattern.length()) {
        throw error("Unclosed character class");
      }
      lastCodePoint = c;
    }

    if (eq != null) {
      result = "(?:" + charClass.toString() + eq.toString() + ")";
    } else {
      result = charClass.toString();
    }

    newPattern.append(result);
    return i;
  }

  /**
   * Given a specific sequence composed of a regular character and
   * combining marks that follow it, produce the alternation that will
   * match all canonical equivalences of that sequence.
   */
  private String produceEquivalentAlternation(String source) {
    int len = countChars(source, 0, 1);
    if (source.length() == len)
    // source has one character.
    {
      return source;
    }

    String base = source.substring(0, len);
    String combiningMarks = source.substring(len);

    String[] perms = producePermutations(combiningMarks);
    StringBuilder result = new StringBuilder(source);

    // Add combined permutations
    for (int x = 0; x < perms.length; x++) {
      String next = base + perms[x];
      if (x > 0) {
        result.append("|" + next);
      }
      next = composeOneStep(next);
      if (next != null) {
        result.append("|" + produceEquivalentAlternation(next));
      }
    }
    return result.toString();
  }

  /**
   * Returns an array of strings that have all the possible
   * permutations of the characters in the input string.
   * This is used to get a list of all possible orderings
   * of a set of combining marks. Note that some of the permutations
   * are invalid because of combining class collisions, and these
   * possibilities must be removed because they are not canonically
   * equivalent.
   */
  private String[] producePermutations(String input) {
    if (input.length() == countChars(input, 0, 1)) {
      return new String[]{input};
    }

    if (input.length() == countChars(input, 0, 2)) {
      int c0 = Character.codePointAt(input, 0);
      int c1 = Character.codePointAt(input, Character.charCount(c0));
      if (getClass(c1) == getClass(c0)) {
        return new String[]{input};
      }
      String[] result = new String[2];
      result[0] = input;
      StringBuilder sb = new StringBuilder(2);
      sb.appendCodePoint(c1);
      sb.appendCodePoint(c0);
      result[1] = sb.toString();
      return result;
    }

    int length = 1;
    int nCodePoints = countCodePoints(input);
    for (int x = 1; x < nCodePoints; x++) {
      length = length * (x + 1);
    }

    String[] temp = new String[length];

    int combClass[] = new int[nCodePoints];
    for (int x = 0, i = 0; x < nCodePoints; x++) {
      int c = Character.codePointAt(input, i);
      combClass[x] = getClass(c);
      i += Character.charCount(c);
    }

    // For each char, take it out and add the permutations
    // of the remaining chars
    int index = 0;
    int len;
    // offset maintains the index in code units.
    loop:
    for (int x = 0, offset = 0; x < nCodePoints; x++, offset += len) {
      len = countChars(input, offset, 1);
      boolean skip = false;
      for (int y = x - 1; y >= 0; y--) {
        if (combClass[y] == combClass[x]) {
          continue loop;
        }
      }
      StringBuilder sb = new StringBuilder(input);
      String otherChars = sb.delete(offset, offset + len).toString();
      String[] subResult = producePermutations(otherChars);

      String prefix = input.substring(offset, offset + len);
      for (int y = 0; y < subResult.length; y++) {
        temp[index++] = prefix + subResult[y];
      }
    }
    String[] result = new String[index];
    for (int x = 0; x < index; x++) {
      result[x] = temp[x];
    }
    return result;
  }

  private int getClass(int c) {
    return sun.text.Normalizer.getCombiningClass(c);
  }

  /**
   * Attempts to compose input by combining the first character
   * with the first combining mark following it. Returns a String
   * that is the composition of the leading character with its first
   * combining mark followed by the remaining combining marks. Returns
   * null if the first two characters cannot be further composed.
   */
  private String composeOneStep(String input) {
    int len = countChars(input, 0, 2);
    String firstTwoCharacters = input.substring(0, len);
    String result = Normalizer.normalize(firstTwoCharacters, Normalizer.Form.NFC);

    if (result.equals(firstTwoCharacters)) {
      return null;
    } else {
      String remainder = input.substring(len);
      return result + remainder;
    }
  }

  /**
   * Preprocess any \Q...\E sequences in `temp', meta-quoting them.
   * See the description of `quotemeta' in perlfunc(1).
   */
  private void RemoveQEQuoting() {
    final int pLen = patternLength;
    int i = 0;
    while (i < pLen - 1) {
      if (temp[i] != '\\') {
        i += 1;
      } else if (temp[i + 1] != 'Q') {
        i += 2;
      } else {
        break;
      }
    }
    if (i >= pLen - 1)    // No \Q sequence found
    {
      return;
    }
    int j = i;
    i += 2;
    int[] newtemp = new int[j + 3 * (pLen - i) + 2];
    System.arraycopy(temp, 0, newtemp, 0, j);

    boolean inQuote = true;
    boolean beginQuote = true;
    while (i < pLen) {
      int c = temp[i++];
      if (!ASCII.isAscii(c) || ASCII.isAlpha(c)) {
        newtemp[j++] = c;
      } else if (ASCII.isDigit(c)) {
        if (beginQuote) {
                    /*
                     * A unicode escape \[0xu] could be before this quote,
                     * and we don't want this numeric char to processed as
                     * part of the escape.
                     */
          newtemp[j++] = '\\';
          newtemp[j++] = 'x';
          newtemp[j++] = '3';
        }
        newtemp[j++] = c;
      } else if (c != '\\') {
        if (inQuote) {
          newtemp[j++] = '\\';
        }
        newtemp[j++] = c;
      } else if (inQuote) {
        if (temp[i] == 'E') {
          i++;
          inQuote = false;
        } else {
          newtemp[j++] = '\\';
          newtemp[j++] = '\\';
        }
      } else {
        if (temp[i] == 'Q') {
          i++;
          inQuote = true;
          beginQuote = true;
          continue;
        } else {
          newtemp[j++] = c;
          if (i != pLen) {
            newtemp[j++] = temp[i++];
          }
        }
      }

      beginQuote = false;
    }

    patternLength = j;
    temp = Arrays.copyOf(newtemp, j + 2); // double zero termination
  }

  /**
   * Copies regular expression to an int array and invokes the parsing
   * of the expression which will create the object tree.
   */
  private void compile() {
    // Handle canonical equivalences
    if (has(CANON_EQ) && !has(LITERAL)) {
      normalize();
    } else {
      normalizedPattern = pattern;
    }
    patternLength = normalizedPattern.length();

    // Copy pattern to int array for convenience
    // Use double zero to terminate pattern
    temp = new int[patternLength + 2];

    hasSupplementary = false;
    int c, count = 0;
    // Convert all chars into code points
    for (int x = 0; x < patternLength; x += Character.charCount(c)) {
      c = normalizedPattern.codePointAt(x);
      if (isSupplementary(c)) {
        hasSupplementary = true;
      }
      temp[count++] = c;
    }

    patternLength = count;   // patternLength now in code points

    if (!has(LITERAL)) {
      RemoveQEQuoting();
    }

    // Allocate all temporary objects here.
    buffer = new int[32];
    groupNodes = new GroupHead[10];
    namedGroups = null;

    if (has(LITERAL)) {
      // Literal pattern handling
      matchRoot = newSlice(temp, patternLength, hasSupplementary);
      matchRoot.next = lastAccept;
    } else {
      // Start recursive descent parsing
      matchRoot = expr(lastAccept);
      // Check extra pattern characters
      if (patternLength != cursor) {
        if (peek() == ')') {
          throw error("Unmatched closing ')'");
        } else {
          throw error("Unexpected internal error");
        }
      }
    }

    // Peephole optimization
    if (matchRoot instanceof Slice) {
      root = BnM.optimize(matchRoot);
      if (root == matchRoot) {
        root = hasSupplementary ? new StartS(matchRoot) : new Start(matchRoot);
      }
    } else if (matchRoot instanceof Begin || matchRoot instanceof First) {
      root = matchRoot;
    } else {
      root = hasSupplementary ? new StartS(matchRoot) : new Start(matchRoot);
    }

    // Release temporary storage
    temp = null;
    buffer = null;
    groupNodes = null;
    patternLength = 0;
    compiled = true;
  }

  Map<String, Integer> namedGroups() {
    if (namedGroups == null) {
      namedGroups = new HashMap<>(2);
    }
    return namedGroups;
  }

  /**
   * Used to print out a subtree of the Pattern to help with debugging.
   */
  private static void printObjectTree(Node node) {
    while (node != null) {
      if (node instanceof Prolog) {
        System.out.println(node);
        printObjectTree(((Prolog) node).loop);
        System.out.println("**** end contents prolog loop");
      } else if (node instanceof Loop) {
        System.out.println(node);
        printObjectTree(((Loop) node).body);
        System.out.println("**** end contents Loop body");
      } else if (node instanceof Curly) {
        System.out.println(node);
        printObjectTree(((Curly) node).atom);
        System.out.println("**** end contents Curly body");
      } else if (node instanceof GroupCurly) {
        System.out.println(node);
        printObjectTree(((GroupCurly) node).atom);
        System.out.println("**** end contents GroupCurly body");
      } else if (node instanceof GroupTail) {
        System.out.println(node);
        System.out.println("Tail next is " + node.next);
        return;
      } else {
        System.out.println(node);
      }
      node = node.next;
      if (node != null) {
        System.out.println("->next:");
      }
      if (node == Pattern.accept) {
        System.out.println("Accept Node");
        node = null;
      }
    }
  }

  /**
   * Used to accumulate information about a subtree of the object graph
   * so that optimizations can be applied to the subtree.
   */
  static final class TreeInfo {

    int minLength;
    int maxLength;
    boolean maxValid;
    boolean deterministic;

    TreeInfo() {
      reset();
    }

    void reset() {
      minLength = 0;
      maxLength = 0;
      maxValid = true;
      deterministic = true;
    }
  }

    /*
     * The following private methods are mainly used to improve the
     * readability of the code. In order to let the Java compiler easily
     * inline them, we should not put many assertions or error checks in them.
     */

  /**
   * Indicates whether a particular flag is set or not.
   */
  private boolean has(int f) {
    return (flags & f) != 0;
  }

  /**
   * Match next character, signal error if failed.
   */
  private void accept(int ch, String s) {
    int testChar = temp[cursor++];
    if (has(COMMENTS)) {
      testChar = parsePastWhitespace(testChar);
    }
    if (ch != testChar) {
      throw error(s);
    }
  }

  /**
   * Mark the end of pattern with a specific character.
   */
  private void mark(int c) {
    temp[patternLength] = c;
  }

  /**
   * Peek the next character, and do not advance the cursor.
   */
  private int peek() {
    int ch = temp[cursor];
    if (has(COMMENTS)) {
      ch = peekPastWhitespace(ch);
    }
    return ch;
  }

  /**
   * Read the next character, and advance the cursor by one.
   */
  private int read() {
    int ch = temp[cursor++];
    if (has(COMMENTS)) {
      ch = parsePastWhitespace(ch);
    }
    return ch;
  }

  /**
   * Read the next character, and advance the cursor by one,
   * ignoring the COMMENTS setting
   */
  private int readEscaped() {
    int ch = temp[cursor++];
    return ch;
  }

  /**
   * Advance the cursor by one, and peek the next character.
   */
  private int next() {
    int ch = temp[++cursor];
    if (has(COMMENTS)) {
      ch = peekPastWhitespace(ch);
    }
    return ch;
  }

  /**
   * Advance the cursor by one, and peek the next character,
   * ignoring the COMMENTS setting
   */
  private int nextEscaped() {
    int ch = temp[++cursor];
    return ch;
  }

  /**
   * If in xmode peek past whitespace and comments.
   */
  private int peekPastWhitespace(int ch) {
    while (ASCII.isSpace(ch) || ch == '#') {
      while (ASCII.isSpace(ch)) {
        ch = temp[++cursor];
      }
      if (ch == '#') {
        ch = peekPastLine();
      }
    }
    return ch;
  }

  /**
   * If in xmode parse past whitespace and comments.
   */
  private int parsePastWhitespace(int ch) {
    while (ASCII.isSpace(ch) || ch == '#') {
      while (ASCII.isSpace(ch)) {
        ch = temp[cursor++];
      }
      if (ch == '#') {
        ch = parsePastLine();
      }
    }
    return ch;
  }

  /**
   * xmode parse past comment to end of line.
   */
  private int parsePastLine() {
    int ch = temp[cursor++];
    while (ch != 0 && !isLineSeparator(ch)) {
      ch = temp[cursor++];
    }
    return ch;
  }

  /**
   * xmode peek past comment to end of line.
   */
  private int peekPastLine() {
    int ch = temp[++cursor];
    while (ch != 0 && !isLineSeparator(ch)) {
      ch = temp[++cursor];
    }
    return ch;
  }

  /**
   * Determines if character is a line separator in the current mode
   */
  private boolean isLineSeparator(int ch) {
    if (has(UNIX_LINES)) {
      return ch == '\n';
    } else {
      return (ch == '\n' ||
          ch == '\r' ||
          (ch | 1) == '\u2029' ||
          ch == '\u0085');
    }
  }

  /**
   * Read the character after the next one, and advance the cursor by two.
   */
  private int skip() {
    int i = cursor;
    int ch = temp[i + 1];
    cursor = i + 2;
    return ch;
  }

  /**
   * Unread one next character, and retreat cursor by one.
   */
  private void unread() {
    cursor--;
  }

  /**
   * Internal method used for handling all syntax errors. The pattern is
   * displayed with a pointer to aid in locating the syntax error.
   */
  private PatternSyntaxException error(String s) {
    return new PatternSyntaxException(s, normalizedPattern, cursor - 1);
  }

  /**
   * Determines if there is any supplementary character or unpaired
   * surrogate in the specified range.
   */
  private boolean findSupplementary(int start, int end) {
    for (int i = start; i < end; i++) {
      if (isSupplementary(temp[i])) {
        return true;
      }
    }
    return false;
  }

  /**
   * Determines if the specified code point is a supplementary
   * character or unpaired surrogate.
   */
  private static final boolean isSupplementary(int ch) {
    return ch >= Character.MIN_SUPPLEMENTARY_CODE_POINT ||
        Character.isSurrogate((char) ch);
  }

  /**
   *  The following methods handle the main parsing. They are sorted
   *  according to their precedence order, the lowest one first.
   */

  /**
   * The expression is parsed with branch nodes added for alternations.
   * This may be called recursively to parse sub expressions that may
   * contain alternations.
   */
  private Node expr(Node end) {
    Node prev = null;
    Node firstTail = null;
    Branch branch = null;
    Node branchConn = null;

    for (; ; ) {
      Node node = sequence(end);
      Node nodeTail = root;      //double return
      if (prev == null) {
        prev = node;
        firstTail = nodeTail;
      } else {
        // Branch
        if (branchConn == null) {
          branchConn = new BranchConn();
          branchConn.next = end;
        }
        if (node == end) {
          // if the node returned from sequence() is "end"
          // we have an empty expr, set a null atom into
          // the branch to indicate to go "next" directly.
          node = null;
        } else {
          // the "tail.next" of each atom goes to branchConn
          nodeTail.next = branchConn;
        }
        if (prev == branch) {
          branch.add(node);
        } else {
          if (prev == end) {
            prev = null;
          } else {
            // replace the "end" with "branchConn" at its tail.next
            // when put the "prev" into the branch as the first atom.
            firstTail.next = branchConn;
          }
          prev = branch = new Branch(prev, node, branchConn);
        }
      }
      if (peek() != '|') {
        return prev;
      }
      next();
    }
  }

  @SuppressWarnings("fallthrough")
  /**
   * Parsing of sequences between alternations.
   */
  private Node sequence(Node end) {
    Node head = null;
    Node tail = null;
    Node node = null;
    LOOP:
    for (; ; ) {
      int ch = peek();
      switch (ch) {
        case '(':
          // Because group handles its own closure,
          // we need to treat it differently
          node = group0();
          // Check for comment or flag group
          if (node == null) {
            continue;
          }
          if (head == null) {
            head = node;
          } else {
            tail.next = node;
          }
          // Double return: Tail was returned in root
          tail = root;
          continue;
        case '[':
          node = clazz(true);
          break;
        case '\\':
          ch = nextEscaped();
          if (ch == 'p' || ch == 'P') {
            boolean oneLetter = true;
            boolean comp = (ch == 'P');
            ch = next(); // Consume { if present
            if (ch != '{') {
              unread();
            } else {
              oneLetter = false;
            }
            node = family(oneLetter, comp);
          } else {
            unread();
            node = atom();
          }
          break;
        case '^':
          next();
          if (has(MULTILINE)) {
            if (has(UNIX_LINES)) {
              node = new UnixCaret();
            } else {
              node = new Caret();
            }
          } else {
            node = new Begin();
          }
          break;
        case '$':
          next();
          if (has(UNIX_LINES)) {
            node = new UnixDollar(has(MULTILINE));
          } else {
            node = new Dollar(has(MULTILINE));
          }
          break;
        case '.':
          next();
          if (has(DOTALL)) {
            node = new All();
          } else {
            if (has(UNIX_LINES)) {
              node = new UnixDot();
            } else {
              node = new Dot();
            }
          }
          break;
        case '|':
        case ')':
          break LOOP;
        case ']': // Now interpreting dangling ] and } as literals
        case '}':
          node = atom();
          break;
        case '?':
        case '*':
        case '+':
          next();
          throw error("Dangling meta character '" + ((char) ch) + "'");
        case 0:
          if (cursor >= patternLength) {
            break LOOP;
          }
          // Fall through
        default:
          node = atom();
          break;
      }

      node = closure(node);

      if (head == null) {
        head = tail = node;
      } else {
        tail.next = node;
        tail = node;
      }
    }
    if (head == null) {
      return end;
    }
    tail.next = end;
    root = tail;      //double return
    return head;
  }

  @SuppressWarnings("fallthrough")
  /**
   * Parse and add a new Single or Slice.
   */
  private Node atom() {
    int first = 0;
    int prev = -1;
    boolean hasSupplementary = false;
    int ch = peek();
    for (; ; ) {
      switch (ch) {
        case '*':
        case '+':
        case '?':
        case '{':
          if (first > 1) {
            cursor = prev;    // Unwind one character
            first--;
          }
          break;
        case '$':
        case '.':
        case '^':
        case '(':
        case '[':
        case '|':
        case ')':
          break;
        case '\\':
          ch = nextEscaped();
          if (ch == 'p' || ch == 'P') { // Property
            if (first > 0) { // Slice is waiting; handle it first
              unread();
              break;
            } else { // No slice; just return the family node
              boolean comp = (ch == 'P');
              boolean oneLetter = true;
              ch = next(); // Consume { if present
              if (ch != '{') {
                unread();
              } else {
                oneLetter = false;
              }
              return family(oneLetter, comp);
            }
          }
          unread();
          prev = cursor;
          ch = escape(false, first == 0, false);
          if (ch >= 0) {
            append(ch, first);
            first++;
            if (isSupplementary(ch)) {
              hasSupplementary = true;
            }
            ch = peek();
            continue;
          } else if (first == 0) {
            return root;
          }
          // Unwind meta escape sequence
          cursor = prev;
          break;
        case 0:
          if (cursor >= patternLength) {
            break;
          }
          // Fall through
        default:
          prev = cursor;
          append(ch, first);
          first++;
          if (isSupplementary(ch)) {
            hasSupplementary = true;
          }
          ch = next();
          continue;
      }
      break;
    }
    if (first == 1) {
      return newSingle(buffer[0]);
    } else {
      return newSlice(buffer, first, hasSupplementary);
    }
  }

  private void append(int ch, int len) {
    if (len >= buffer.length) {
      int[] tmp = new int[len + len];
      System.arraycopy(buffer, 0, tmp, 0, len);
      buffer = tmp;
    }
    buffer[len] = ch;
  }

  /**
   * Parses a backref greedily, taking as many numbers as it
   * can. The first digit is always treated as a backref, but
   * multi digit numbers are only treated as a backref if at
   * least that many backrefs exist at this point in the regex.
   */
  private Node ref(int refNum) {
    boolean done = false;
    while (!done) {
      int ch = peek();
      switch (ch) {
        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
          int newRefNum = (refNum * 10) + (ch - '0');
          // Add another number if it doesn't make a group
          // that doesn't exist
          if (capturingGroupCount - 1 < newRefNum) {
            done = true;
            break;
          }
          refNum = newRefNum;
          read();
          break;
        default:
          done = true;
          break;
      }
    }
    if (has(CASE_INSENSITIVE)) {
      return new CIBackRef(refNum, has(UNICODE_CASE));
    } else {
      return new BackRef(refNum);
    }
  }

  /**
   * Parses an escape sequence to determine the actual value that needs
   * to be matched.
   * If -1 is returned and create was true a new object was added to the tree
   * to handle the escape sequence.
   * If the returned value is greater than zero, it is the value that
   * matches the escape sequence.
   */
  private int escape(boolean inclass, boolean create, boolean isrange) {
    int ch = skip();
    switch (ch) {
      case '0':
        return o();
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
      case '8':
      case '9':
        if (inclass) {
          break;
        }
        if (create) {
          root = ref((ch - '0'));
        }
        return -1;
      case 'A':
        if (inclass) {
          break;
        }
        if (create) {
          root = new Begin();
        }
        return -1;
      case 'B':
        if (inclass) {
          break;
        }
        if (create) {
          root = new Bound(Bound.NONE, has(UNICODE_CHARACTER_CLASS));
        }
        return -1;
      case 'C':
        break;
      case 'D':
        if (create) {
          root = has(UNICODE_CHARACTER_CLASS)
              ? new Utype(UnicodeProp.DIGIT).complement()
              : new Ctype(ASCII.DIGIT).complement();
        }
        return -1;
      case 'E':
      case 'F':
        break;
      case 'G':
        if (inclass) {
          break;
        }
        if (create) {
          root = new LastMatch();
        }
        return -1;
      case 'H':
        if (create) {
          root = new HorizWS().complement();
        }
        return -1;
      case 'I':
      case 'J':
      case 'K':
      case 'L':
      case 'M':
      case 'N':
      case 'O':
      case 'P':
      case 'Q':
        break;
      case 'R':
        if (inclass) {
          break;
        }
        if (create) {
          root = new LineEnding();
        }
        return -1;
      case 'S':
        if (create) {
          root = has(UNICODE_CHARACTER_CLASS)
              ? new Utype(UnicodeProp.WHITE_SPACE).complement()
              : new Ctype(ASCII.SPACE).complement();
        }
        return -1;
      case 'T':
      case 'U':
        break;
      case 'V':
        if (create) {
          root = new VertWS().complement();
        }
        return -1;
      case 'W':
        if (create) {
          root = has(UNICODE_CHARACTER_CLASS)
              ? new Utype(UnicodeProp.WORD).complement()
              : new Ctype(ASCII.WORD).complement();
        }
        return -1;
      case 'X':
      case 'Y':
        break;
      case 'Z':
        if (inclass) {
          break;
        }
        if (create) {
          if (has(UNIX_LINES)) {
            root = new UnixDollar(false);
          } else {
            root = new Dollar(false);
          }
        }
        return -1;
      case 'a':
        return '\007';
      case 'b':
        if (inclass) {
          break;
        }
        if (create) {
          root = new Bound(Bound.BOTH, has(UNICODE_CHARACTER_CLASS));
        }
        return -1;
      case 'c':
        return c();
      case 'd':
        if (create) {
          root = has(UNICODE_CHARACTER_CLASS)
              ? new Utype(UnicodeProp.DIGIT)
              : new Ctype(ASCII.DIGIT);
        }
        return -1;
      case 'e':
        return '\033';
      case 'f':
        return '\f';
      case 'g':
        break;
      case 'h':
        if (create) {
          root = new HorizWS();
        }
        return -1;
      case 'i':
      case 'j':
        break;
      case 'k':
        if (inclass) {
          break;
        }
        if (read() != '<') {
          throw error("\\k is not followed by '<' for named capturing group");
        }
        String name = groupname(read());
        if (!namedGroups().containsKey(name)) {
          throw error("(named capturing group <" + name + "> does not exit");
        }
        if (create) {
          if (has(CASE_INSENSITIVE)) {
            root = new CIBackRef(namedGroups().get(name), has(UNICODE_CASE));
          } else {
            root = new BackRef(namedGroups().get(name));
          }
        }
        return -1;
      case 'l':
      case 'm':
        break;
      case 'n':
        return '\n';
      case 'o':
      case 'p':
      case 'q':
        break;
      case 'r':
        return '\r';
      case 's':
        if (create) {
          root = has(UNICODE_CHARACTER_CLASS)
              ? new Utype(UnicodeProp.WHITE_SPACE)
              : new Ctype(ASCII.SPACE);
        }
        return -1;
      case 't':
        return '\t';
      case 'u':
        return u();
      case 'v':
        // '\v' was implemented as VT/0x0B in releases < 1.8 (though
        // undocumented). In JDK8 '\v' is specified as a predefined
        // character class for all vertical whitespace characters.
        // So [-1, root=VertWS node] pair is returned (instead of a
        // single 0x0B). This breaks the range if '\v' is used as
        // the start or end value, such as [\v-...] or [...-\v], in
        // which a single definite value (0x0B) is expected. For
        // compatibility concern '\013'/0x0B is returned if isrange.
        if (isrange) {
          return '\013';
        }
        if (create) {
          root = new VertWS();
        }
        return -1;
      case 'w':
        if (create) {
          root = has(UNICODE_CHARACTER_CLASS)
              ? new Utype(UnicodeProp.WORD)
              : new Ctype(ASCII.WORD);
        }
        return -1;
      case 'x':
        return x();
      case 'y':
        break;
      case 'z':
        if (inclass) {
          break;
        }
        if (create) {
          root = new End();
        }
        return -1;
      default:
        return ch;
    }
    throw error("Illegal/unsupported escape sequence");
  }

  /**
   * Parse a character class, and return the node that matches it.
   *
   * Consumes a ] on the way out if consume is true. Usually consume
   * is true except for the case of [abc&&def] where def is a separate
   * right hand node with "understood" brackets.
   */
  private CharProperty clazz(boolean consume) {
    CharProperty prev = null;
    CharProperty node = null;
    BitClass bits = new BitClass();
    boolean include = true;
    boolean firstInClass = true;
    int ch = next();
    for (; ; ) {
      switch (ch) {
        case '^':
          // Negates if first char in a class, otherwise literal
          if (firstInClass) {
            if (temp[cursor - 1] != '[') {
              break;
            }
            ch = next();
            include = !include;
            continue;
          } else {
            // ^ not first in class, treat as literal
            break;
          }
        case '[':
          firstInClass = false;
          node = clazz(true);
          if (prev == null) {
            prev = node;
          } else {
            prev = union(prev, node);
          }
          ch = peek();
          continue;
        case '&':
          firstInClass = false;
          ch = next();
          if (ch == '&') {
            ch = next();
            CharProperty rightNode = null;
            while (ch != ']' && ch != '&') {
              if (ch == '[') {
                if (rightNode == null) {
                  rightNode = clazz(true);
                } else {
                  rightNode = union(rightNode, clazz(true));
                }
              } else { // abc&&def
                unread();
                rightNode = clazz(false);
              }
              ch = peek();
            }
            if (rightNode != null) {
              node = rightNode;
            }
            if (prev == null) {
              if (rightNode == null) {
                throw error("Bad class syntax");
              } else {
                prev = rightNode;
              }
            } else {
              prev = intersection(prev, node);
            }
          } else {
            // treat as a literal &
            unread();
            break;
          }
          continue;
        case 0:
          firstInClass = false;
          if (cursor >= patternLength) {
            throw error("Unclosed character class");
          }
          break;
        case ']':
          firstInClass = false;
          if (prev != null) {
            if (consume) {
              next();
            }
            return prev;
          }
          break;
        default:
          firstInClass = false;
          break;
      }
      node = range(bits);
      if (include) {
        if (prev == null) {
          prev = node;
        } else {
          if (prev != node) {
            prev = union(prev, node);
          }
        }
      } else {
        if (prev == null) {
          prev = node.complement();
        } else {
          if (prev != node) {
            prev = setDifference(prev, node);
          }
        }
      }
      ch = peek();
    }
  }

  private CharProperty bitsOrSingle(BitClass bits, int ch) {
        /* Bits can only handle codepoints in [u+0000-u+00ff] range.
           Use "single" node instead of bits when dealing with unicode
           case folding for codepoints listed below.
           (1)Uppercase out of range: u+00ff, u+00b5
              toUpperCase(u+00ff) -> u+0178
              toUpperCase(u+00b5) -> u+039c
           (2)LatinSmallLetterLongS u+17f
              toUpperCase(u+017f) -> u+0053
           (3)LatinSmallLetterDotlessI u+131
              toUpperCase(u+0131) -> u+0049
           (4)LatinCapitalLetterIWithDotAbove u+0130
              toLowerCase(u+0130) -> u+0069
           (5)KelvinSign u+212a
              toLowerCase(u+212a) ==> u+006B
           (6)AngstromSign u+212b
              toLowerCase(u+212b) ==> u+00e5
        */
    int d;
    if (ch < 256 &&
        !(has(CASE_INSENSITIVE) && has(UNICODE_CASE) &&
            (ch == 0xff || ch == 0xb5 ||
                ch == 0x49 || ch == 0x69 ||  //I and i
                ch == 0x53 || ch == 0x73 ||  //S and s
                ch == 0x4b || ch == 0x6b ||  //K and k
                ch == 0xc5 || ch == 0xe5)))  //A+ring
    {
      return bits.add(ch, flags());
    }
    return newSingle(ch);
  }

  /**
   * Parse a single character or a character range in a character class
   * and return its representative node.
   */
  private CharProperty range(BitClass bits) {
    int ch = peek();
    if (ch == '\\') {
      ch = nextEscaped();
      if (ch == 'p' || ch == 'P') { // A property
        boolean comp = (ch == 'P');
        boolean oneLetter = true;
        // Consume { if present
        ch = next();
        if (ch != '{') {
          unread();
        } else {
          oneLetter = false;
        }
        return family(oneLetter, comp);
      } else { // ordinary escape
        boolean isrange = temp[cursor + 1] == '-';
        unread();
        ch = escape(true, true, isrange);
        if (ch == -1) {
          return (CharProperty) root;
        }
      }
    } else {
      next();
    }
    if (ch >= 0) {
      if (peek() == '-') {
        int endRange = temp[cursor + 1];
        if (endRange == '[') {
          return bitsOrSingle(bits, ch);
        }
        if (endRange != ']') {
          next();
          int m = peek();
          if (m == '\\') {
            m = escape(true, false, true);
          } else {
            next();
          }
          if (m < ch) {
            throw error("Illegal character range");
          }
          if (has(CASE_INSENSITIVE)) {
            return caseInsensitiveRangeFor(ch, m);
          } else {
            return rangeFor(ch, m);
          }
        }
      }
      return bitsOrSingle(bits, ch);
    }
    throw error("Unexpected character '" + ((char) ch) + "'");
  }

  /**
   * Parses a Unicode character family and returns its representative node.
   */
  private CharProperty family(boolean singleLetter,
      boolean maybeComplement) {
    next();
    String name;
    CharProperty node = null;

    if (singleLetter) {
      int c = temp[cursor];
      if (!Character.isSupplementaryCodePoint(c)) {
        name = String.valueOf((char) c);
      } else {
        name = new String(temp, cursor, 1);
      }
      read();
    } else {
      int i = cursor;
      mark('}');
      while (read() != '}') {
      }
      mark('\000');
      int j = cursor;
      if (j > patternLength) {
        throw error("Unclosed character family");
      }
      if (i + 1 >= j) {
        throw error("Empty character family");
      }
      name = new String(temp, i, j - i - 1);
    }

    int i = name.indexOf('=');
    if (i != -1) {
      // property construct \p{name=value}
      String value = name.substring(i + 1);
      name = name.substring(0, i).toLowerCase(Locale.ENGLISH);
      if ("sc".equals(name) || "script".equals(name)) {
        node = unicodeScriptPropertyFor(value);
      } else if ("blk".equals(name) || "block".equals(name)) {
        node = unicodeBlockPropertyFor(value);
      } else if ("gc".equals(name) || "general_category".equals(name)) {
        node = charPropertyNodeFor(value);
      } else {
        throw error("Unknown Unicode property {name=<" + name + ">, "
            + "value=<" + value + ">}");
      }
    } else {
      if (name.startsWith("In")) {
        // \p{inBlockName}
        node = unicodeBlockPropertyFor(name.substring(2));
      } else if (name.startsWith("Is")) {
        // \p{isGeneralCategory} and \p{isScriptName}
        name = name.substring(2);
        UnicodeProp uprop = UnicodeProp.forName(name);
        if (uprop != null) {
          node = new Utype(uprop);
        }
        if (node == null) {
          node = CharPropertyNames.charPropertyFor(name);
        }
        if (node == null) {
          node = unicodeScriptPropertyFor(name);
        }
      } else {
        if (has(UNICODE_CHARACTER_CLASS)) {
          UnicodeProp uprop = UnicodeProp.forPOSIXName(name);
          if (uprop != null) {
            node = new Utype(uprop);
          }
        }
        if (node == null) {
          node = charPropertyNodeFor(name);
        }
      }
    }
    if (maybeComplement) {
      if (node instanceof Category || node instanceof Block) {
        hasSupplementary = true;
      }
      node = node.complement();
    }
    return node;
  }


  /**
   * Returns a CharProperty matching all characters belong to
   * a UnicodeScript.
   */
  private CharProperty unicodeScriptPropertyFor(String name) {
    final Character.UnicodeScript script;
    try {
      script = Character.UnicodeScript.forName(name);
    } catch (IllegalArgumentException iae) {
      throw error("Unknown character script name {" + name + "}");
    }
    return new Script(script);
  }

  /**
   * Returns a CharProperty matching all characters in a UnicodeBlock.
   */
  private CharProperty unicodeBlockPropertyFor(String name) {
    final Character.UnicodeBlock block;
    try {
      block = Character.UnicodeBlock.forName(name);
    } catch (IllegalArgumentException iae) {
      throw error("Unknown character block name {" + name + "}");
    }
    return new Block(block);
  }

  /**
   * Returns a CharProperty matching all characters in a named property.
   */
  private CharProperty charPropertyNodeFor(String name) {
    CharProperty p = CharPropertyNames.charPropertyFor(name);
    if (p == null) {
      throw error("Unknown character property name {" + name + "}");
    }
    return p;
  }

  /**
   * Parses and returns the name of a "named capturing group", the trailing
   * ">" is consumed after parsing.
   */
  private String groupname(int ch) {
    StringBuilder sb = new StringBuilder();
    sb.append(Character.toChars(ch));
    while (ASCII.isLower(ch = read()) || ASCII.isUpper(ch) ||
        ASCII.isDigit(ch)) {
      sb.append(Character.toChars(ch));
    }
    if (sb.length() == 0) {
      throw error("named capturing group has 0 length name");
    }
    if (ch != '>') {
      throw error("named capturing group is missing trailing '>'");
    }
    return sb.toString();
  }

  /**
   * Parses a group and returns the head node of a set of nodes that process
   * the group. Sometimes a double return system is used where the tail is
   * returned in root.
   */
  private Node group0() {
    boolean capturingGroup = false;
    Node head = null;
    Node tail = null;
    int save = flags;
    root = null;
    int ch = next();
    if (ch == '?') {
      ch = skip();
      switch (ch) {
        case ':':   //  (?:xxx) pure group
          head = createGroup(true);
          tail = root;
          head.next = expr(tail);
          break;
        case '=':   // (?=xxx) and (?!xxx) lookahead
        case '!':
          head = createGroup(true);
          tail = root;
          head.next = expr(tail);
          if (ch == '=') {
            head = tail = new Pos(head);
          } else {
            head = tail = new Neg(head);
          }
          break;
        case '>':   // (?>xxx)  independent group
          head = createGroup(true);
          tail = root;
          head.next = expr(tail);
          head = tail = new Ques(head, INDEPENDENT);
          break;
        case '<':   // (?<xxx)  look behind
          ch = read();
          if (ASCII.isLower(ch) || ASCII.isUpper(ch)) {
            // named captured group
            String name = groupname(ch);
            if (namedGroups().containsKey(name)) {
              throw error("Named capturing group <" + name
                  + "> is already defined");
            }
            capturingGroup = true;
            head = createGroup(false);
            tail = root;
            namedGroups().put(name, capturingGroupCount - 1);
            head.next = expr(tail);
            break;
          }
          int start = cursor;
          head = createGroup(true);
          tail = root;
          head.next = expr(tail);
          tail.next = lookbehindEnd;
          TreeInfo info = new TreeInfo();
          head.study(info);
          if (info.maxValid == false) {
            throw error("Look-behind group does not have "
                + "an obvious maximum length");
          }
          boolean hasSupplementary = findSupplementary(start, patternLength);
          if (ch == '=') {
            head = tail = (hasSupplementary ?
                new BehindS(head, info.maxLength,
                    info.minLength) :
                new Behind(head, info.maxLength,
                    info.minLength));
          } else if (ch == '!') {
            head = tail = (hasSupplementary ?
                new NotBehindS(head, info.maxLength,
                    info.minLength) :
                new NotBehind(head, info.maxLength,
                    info.minLength));
          } else {
            throw error("Unknown look-behind group");
          }
          break;
        case '$':
        case '@':
          throw error("Unknown group type");
        default:    // (?xxx:) inlined match flags
          unread();
          addFlag();
          ch = read();
          if (ch == ')') {
            return null;    // Inline modifier only
          }
          if (ch != ':') {
            throw error("Unknown inline modifier");
          }
          head = createGroup(true);
          tail = root;
          head.next = expr(tail);
          break;
      }
    } else { // (xxx) a regular group
      capturingGroup = true;
      head = createGroup(false);
      tail = root;
      head.next = expr(tail);
    }

    accept(')', "Unclosed group");
    flags = save;

    // Check for quantifiers
    Node node = closure(head);
    if (node == head) { // No closure
      root = tail;
      return node;    // Dual return
    }
    if (head == tail) { // Zero length assertion
      root = node;
      return node;    // Dual return
    }

    if (node instanceof Ques) {
      Ques ques = (Ques) node;
      if (ques.type == POSSESSIVE) {
        root = node;
        return node;
      }
      tail.next = new BranchConn();
      tail = tail.next;
      if (ques.type == GREEDY) {
        head = new Branch(head, null, tail);
      } else { // Reluctant quantifier
        head = new Branch(null, head, tail);
      }
      root = tail;
      return head;
    } else if (node instanceof Curly) {
      Curly curly = (Curly) node;
      if (curly.type == POSSESSIVE) {
        root = node;
        return node;
      }
      // Discover if the group is deterministic
      TreeInfo info = new TreeInfo();
      if (head.study(info)) { // Deterministic
        GroupTail temp = (GroupTail) tail;
        head = root = new GroupCurly(head.next, curly.cmin,
            curly.cmax, curly.type,
            ((GroupTail) tail).localIndex,
            ((GroupTail) tail).groupIndex,
            capturingGroup);
        return head;
      } else { // Non-deterministic
        int temp = ((GroupHead) head).localIndex;
        Loop loop;
        if (curly.type == GREEDY) {
          loop = new Loop(this.localCount, temp);
        } else  // Reluctant Curly
        {
          loop = new LazyLoop(this.localCount, temp);
        }
        Prolog prolog = new Prolog(loop);
        this.localCount += 1;
        loop.cmin = curly.cmin;
        loop.cmax = curly.cmax;
        loop.body = head;
        tail.next = loop;
        root = loop;
        return prolog; // Dual return
      }
    }
    throw error("Internal logic error");
  }

  /**
   * Create group head and tail nodes using double return. If the group is
   * created with anonymous true then it is a pure group and should not
   * affect group counting.
   */
  private Node createGroup(boolean anonymous) {
    int localIndex = localCount++;
    int groupIndex = 0;
    if (!anonymous) {
      groupIndex = capturingGroupCount++;
    }
    GroupHead head = new GroupHead(localIndex);
    root = new GroupTail(localIndex, groupIndex);
    if (!anonymous && groupIndex < 10) {
      groupNodes[groupIndex] = head;
    }
    return head;
  }

  @SuppressWarnings("fallthrough")
  /**
   * Parses inlined match flags and set them appropriately.
   */
  private void addFlag() {
    int ch = peek();
    for (; ; ) {
      switch (ch) {
        case 'i':
          flags |= CASE_INSENSITIVE;
          break;
        case 'm':
          flags |= MULTILINE;
          break;
        case 's':
          flags |= DOTALL;
          break;
        case 'd':
          flags |= UNIX_LINES;
          break;
        case 'u':
          flags |= UNICODE_CASE;
          break;
        case 'c':
          flags |= CANON_EQ;
          break;
        case 'x':
          flags |= COMMENTS;
          break;
        case 'U':
          flags |= (UNICODE_CHARACTER_CLASS | UNICODE_CASE);
          break;
        case '-': // subFlag then fall through
          ch = next();
          subFlag();
        default:
          return;
      }
      ch = next();
    }
  }

  @SuppressWarnings("fallthrough")
  /**
   * Parses the second part of inlined match flags and turns off
   * flags appropriately.
   */
  private void subFlag() {
    int ch = peek();
    for (; ; ) {
      switch (ch) {
        case 'i':
          flags &= ~CASE_INSENSITIVE;
          break;
        case 'm':
          flags &= ~MULTILINE;
          break;
        case 's':
          flags &= ~DOTALL;
          break;
        case 'd':
          flags &= ~UNIX_LINES;
          break;
        case 'u':
          flags &= ~UNICODE_CASE;
          break;
        case 'c':
          flags &= ~CANON_EQ;
          break;
        case 'x':
          flags &= ~COMMENTS;
          break;
        case 'U':
          flags &= ~(UNICODE_CHARACTER_CLASS | UNICODE_CASE);
        default:
          return;
      }
      ch = next();
    }
  }

  static final int MAX_REPS = 0x7FFFFFFF;

  static final int GREEDY = 0;

  static final int LAZY = 1;

  static final int POSSESSIVE = 2;

  static final int INDEPENDENT = 3;

  /**
   * Processes repetition. If the next character peeked is a quantifier
   * then new nodes must be appended to handle the repetition.
   * Prev could be a single or a group, so it could be a chain of nodes.
   */
  private Node closure(Node prev) {
    Node atom;
    int ch = peek();
    switch (ch) {
      case '?':
        ch = next();
        if (ch == '?') {
          next();
          return new Ques(prev, LAZY);
        } else if (ch == '+') {
          next();
          return new Ques(prev, POSSESSIVE);
        }
        return new Ques(prev, GREEDY);
      case '*':
        ch = next();
        if (ch == '?') {
          next();
          return new Curly(prev, 0, MAX_REPS, LAZY);
        } else if (ch == '+') {
          next();
          return new Curly(prev, 0, MAX_REPS, POSSESSIVE);
        }
        return new Curly(prev, 0, MAX_REPS, GREEDY);
      case '+':
        ch = next();
        if (ch == '?') {
          next();
          return new Curly(prev, 1, MAX_REPS, LAZY);
        } else if (ch == '+') {
          next();
          return new Curly(prev, 1, MAX_REPS, POSSESSIVE);
        }
        return new Curly(prev, 1, MAX_REPS, GREEDY);
      case '{':
        ch = temp[cursor + 1];
        if (ASCII.isDigit(ch)) {
          skip();
          int cmin = 0;
          do {
            cmin = cmin * 10 + (ch - '0');
          } while (ASCII.isDigit(ch = read()));
          int cmax = cmin;
          if (ch == ',') {
            ch = read();
            cmax = MAX_REPS;
            if (ch != '}') {
              cmax = 0;
              while (ASCII.isDigit(ch)) {
                cmax = cmax * 10 + (ch - '0');
                ch = read();
              }
            }
          }
          if (ch != '}') {
            throw error("Unclosed counted closure");
          }
          if (((cmin) | (cmax) | (cmax - cmin)) < 0) {
            throw error("Illegal repetition range");
          }
          Curly curly;
          ch = peek();
          if (ch == '?') {
            next();
            curly = new Curly(prev, cmin, cmax, LAZY);
          } else if (ch == '+') {
            next();
            curly = new Curly(prev, cmin, cmax, POSSESSIVE);
          } else {
            curly = new Curly(prev, cmin, cmax, GREEDY);
          }
          return curly;
        } else {
          throw error("Illegal repetition");
        }
      default:
        return prev;
    }
  }

  /**
   * Utility method for parsing control escape sequences.
   */
  private int c() {
    if (cursor < patternLength) {
      return read() ^ 64;
    }
    throw error("Illegal control escape sequence");
  }

  /**
   * Utility method for parsing octal escape sequences.
   */
  private int o() {
    int n = read();
    if (((n - '0') | ('7' - n)) >= 0) {
      int m = read();
      if (((m - '0') | ('7' - m)) >= 0) {
        int o = read();
        if ((((o - '0') | ('7' - o)) >= 0) && (((n - '0') | ('3' - n)) >= 0)) {
          return (n - '0') * 64 + (m - '0') * 8 + (o - '0');
        }
        unread();
        return (n - '0') * 8 + (m - '0');
      }
      unread();
      return (n - '0');
    }
    throw error("Illegal octal escape sequence");
  }

  /**
   * Utility method for parsing hexadecimal escape sequences.
   */
  private int x() {
    int n = read();
    if (ASCII.isHexDigit(n)) {
      int m = read();
      if (ASCII.isHexDigit(m)) {
        return ASCII.toDigit(n) * 16 + ASCII.toDigit(m);
      }
    } else if (n == '{' && ASCII.isHexDigit(peek())) {
      int ch = 0;
      while (ASCII.isHexDigit(n = read())) {
        ch = (ch << 4) + ASCII.toDigit(n);
        if (ch > Character.MAX_CODE_POINT) {
          throw error("Hexadecimal codepoint is too big");
        }
      }
      if (n != '}') {
        throw error("Unclosed hexadecimal escape sequence");
      }
      return ch;
    }
    throw error("Illegal hexadecimal escape sequence");
  }

  /**
   * Utility method for parsing unicode escape sequences.
   */
  private int cursor() {
    return cursor;
  }

  private void setcursor(int pos) {
    cursor = pos;
  }

  private int uxxxx() {
    int n = 0;
    for (int i = 0; i < 4; i++) {
      int ch = read();
      if (!ASCII.isHexDigit(ch)) {
        throw error("Illegal Unicode escape sequence");
      }
      n = n * 16 + ASCII.toDigit(ch);
    }
    return n;
  }

  private int u() {
    int n = uxxxx();
    if (Character.isHighSurrogate((char) n)) {
      int cur = cursor();
      if (read() == '\\' && read() == 'u') {
        int n2 = uxxxx();
        if (Character.isLowSurrogate((char) n2)) {
          return Character.toCodePoint((char) n, (char) n2);
        }
      }
      setcursor(cur);
    }
    return n;
  }

  //
  // Utility methods for code point support
  //

  private static final int countChars(CharSequence seq, int index,
      int lengthInCodePoints) {
    // optimization
    if (lengthInCodePoints == 1 && !Character.isHighSurrogate(seq.charAt(index))) {
      assert (index >= 0 && index < seq.length());
      return 1;
    }
    int length = seq.length();
    int x = index;
    if (lengthInCodePoints >= 0) {
      assert (index >= 0 && index < length);
      for (int i = 0; x < length && i < lengthInCodePoints; i++) {
        if (Character.isHighSurrogate(seq.charAt(x++))) {
          if (x < length && Character.isLowSurrogate(seq.charAt(x))) {
            x++;
          }
        }
      }
      return x - index;
    }

    assert (index >= 0 && index <= length);
    if (index == 0) {
      return 0;
    }
    int len = -lengthInCodePoints;
    for (int i = 0; x > 0 && i < len; i++) {
      if (Character.isLowSurrogate(seq.charAt(--x))) {
        if (x > 0 && Character.isHighSurrogate(seq.charAt(x - 1))) {
          x--;
        }
      }
    }
    return index - x;
  }

  private static final int countCodePoints(CharSequence seq) {
    int length = seq.length();
    int n = 0;
    for (int i = 0; i < length; ) {
      n++;
      if (Character.isHighSurrogate(seq.charAt(i++))) {
        if (i < length && Character.isLowSurrogate(seq.charAt(i))) {
          i++;
        }
      }
    }
    return n;
  }

  /**
   * Creates a bit vector for matching Latin-1 values. A normal BitClass
   * never matches values above Latin-1, and a complemented BitClass always
   * matches values above Latin-1.
   */
  private static final class BitClass extends BmpCharProperty {

    final boolean[] bits;

    BitClass() {
      bits = new boolean[256];
    }

    private BitClass(boolean[] bits) {
      this.bits = bits;
    }

    BitClass add(int c, int flags) {
      assert c >= 0 && c <= 255;
      if ((flags & CASE_INSENSITIVE) != 0) {
        if (ASCII.isAscii(c)) {
          bits[ASCII.toUpper(c)] = true;
          bits[ASCII.toLower(c)] = true;
        } else if ((flags & UNICODE_CASE) != 0) {
          bits[Character.toLowerCase(c)] = true;
          bits[Character.toUpperCase(c)] = true;
        }
      }
      bits[c] = true;
      return this;
    }

    boolean isSatisfiedBy(int ch) {
      return ch < 256 && bits[ch];
    }
  }

  /**
   * Returns a suitably optimized, single character matcher.
   */
  private CharProperty newSingle(final int ch) {
    if (has(CASE_INSENSITIVE)) {
      int lower, upper;
      if (has(UNICODE_CASE)) {
        upper = Character.toUpperCase(ch);
        lower = Character.toLowerCase(upper);
        if (upper != lower) {
          return new SingleU(lower);
        }
      } else if (ASCII.isAscii(ch)) {
        lower = ASCII.toLower(ch);
        upper = ASCII.toUpper(ch);
        if (lower != upper) {
          return new SingleI(lower, upper);
        }
      }
    }
    if (isSupplementary(ch)) {
      return new SingleS(ch);    // Match a given Unicode character
    }
    return new Single(ch);         // Match a given BMP character
  }

  /**
   * Utility method for creating a string slice matcher.
   */
  private Node newSlice(int[] buf, int count, boolean hasSupplementary) {
    int[] tmp = new int[count];
    if (has(CASE_INSENSITIVE)) {
      if (has(UNICODE_CASE)) {
        for (int i = 0; i < count; i++) {
          tmp[i] = Character.toLowerCase(
              Character.toUpperCase(buf[i]));
        }
        return hasSupplementary ? new SliceUS(tmp) : new SliceU(tmp);
      }
      for (int i = 0; i < count; i++) {
        tmp[i] = ASCII.toLower(buf[i]);
      }
      return hasSupplementary ? new SliceIS(tmp) : new SliceI(tmp);
    }
    for (int i = 0; i < count; i++) {
      tmp[i] = buf[i];
    }
    return hasSupplementary ? new SliceS(tmp) : new Slice(tmp);
  }

  /**
   * The following classes are the building components of the object
   * tree that represents a compiled regular expression. The object tree
   * is made of individual elements that handle constructs in the Pattern.
   * Each type of object knows how to match its equivalent construct with
   * the match() method.
   */

  /**
   * Base class for all node classes. Subclasses should override the match()
   * method as appropriate. This class is an accepting node, so its match()
   * always returns true.
   */
  static class Node extends Object {

    Node next;

    Node() {
      next = Pattern.accept;
    }

    /**
     * This method implements the classic accept node.
     */
    boolean match(Matcher matcher, int i, CharSequence seq) {
      matcher.last = i;
      matcher.groups[0] = matcher.first;
      matcher.groups[1] = matcher.last;
      return true;
    }

    /**
     * This method is good for all zero length assertions.
     */
    boolean study(TreeInfo info) {
      if (next != null) {
        return next.study(info);
      } else {
        return info.deterministic;
      }
    }
  }

  static class LastNode extends Node {

    /**
     * This method implements the classic accept node with
     * the addition of a check to see if the match occurred
     * using all of the input.
     */
    boolean match(Matcher matcher, int i, CharSequence seq) {
      if (matcher.acceptMode == Matcher.ENDANCHOR && i != matcher.to) {
        return false;
      }
      matcher.last = i;
      matcher.groups[0] = matcher.first;
      matcher.groups[1] = matcher.last;
      return true;
    }
  }

  /**
   * Used for REs that can start anywhere within the input string.
   * This basically tries to match repeatedly at each spot in the
   * input string, moving forward after each try. An anchored search
   * or a BnM will bypass this node completely.
   */
  static class Start extends Node {

    int minLength;

    Start(Node node) {
      this.next = node;
      TreeInfo info = new TreeInfo();
      next.study(info);
      minLength = info.minLength;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      if (i > matcher.to - minLength) {
        matcher.hitEnd = true;
        return false;
      }
      int guard = matcher.to - minLength;
      for (; i <= guard; i++) {
        if (next.match(matcher, i, seq)) {
          matcher.first = i;
          matcher.groups[0] = matcher.first;
          matcher.groups[1] = matcher.last;
          return true;
        }
      }
      matcher.hitEnd = true;
      return false;
    }

    boolean study(TreeInfo info) {
      next.study(info);
      info.maxValid = false;
      info.deterministic = false;
      return false;
    }
  }

  /*
     * StartS supports supplementary characters, including unpaired surrogates.
     */
  static final class StartS extends Start {

    StartS(Node node) {
      super(node);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      if (i > matcher.to - minLength) {
        matcher.hitEnd = true;
        return false;
      }
      int guard = matcher.to - minLength;
      while (i <= guard) {
        //if ((ret = next.match(matcher, i, seq)) || i == guard)
        if (next.match(matcher, i, seq)) {
          matcher.first = i;
          matcher.groups[0] = matcher.first;
          matcher.groups[1] = matcher.last;
          return true;
        }
        if (i == guard) {
          break;
        }
        // Optimization to move to the next character. This is
        // faster than countChars(seq, i, 1).
        if (Character.isHighSurrogate(seq.charAt(i++))) {
          if (i < seq.length() &&
              Character.isLowSurrogate(seq.charAt(i))) {
            i++;
          }
        }
      }
      matcher.hitEnd = true;
      return false;
    }
  }

  /**
   * Node to anchor at the beginning of input. This object implements the
   * match for a \A sequence, and the caret anchor will use this if not in
   * multiline mode.
   */
  static final class Begin extends Node {

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int fromIndex = (matcher.anchoringBounds) ?
          matcher.from : 0;
      if (i == fromIndex && next.match(matcher, i, seq)) {
        matcher.first = i;
        matcher.groups[0] = i;
        matcher.groups[1] = matcher.last;
        return true;
      } else {
        return false;
      }
    }
  }

  /**
   * Node to anchor at the end of input. This is the absolute end, so this
   * should not match at the last newline before the end as $ will.
   */
  static final class End extends Node {

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int endIndex = (matcher.anchoringBounds) ?
          matcher.to : matcher.getTextLength();
      if (i == endIndex) {
        matcher.hitEnd = true;
        return next.match(matcher, i, seq);
      }
      return false;
    }
  }

  /**
   * Node to anchor at the beginning of a line. This is essentially the
   * object to match for the multiline ^.
   */
  static final class Caret extends Node {

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int startIndex = matcher.from;
      int endIndex = matcher.to;
      if (!matcher.anchoringBounds) {
        startIndex = 0;
        endIndex = matcher.getTextLength();
      }
      // Perl does not match ^ at end of input even after newline
      if (i == endIndex) {
        matcher.hitEnd = true;
        return false;
      }
      if (i > startIndex) {
        char ch = seq.charAt(i - 1);
        if (ch != '\n' && ch != '\r'
            && (ch | 1) != '\u2029'
            && ch != '\u0085') {
          return false;
        }
        // Should treat /r/n as one newline
        if (ch == '\r' && seq.charAt(i) == '\n') {
          return false;
        }
      }
      return next.match(matcher, i, seq);
    }
  }

  /**
   * Node to anchor at the beginning of a line when in unixdot mode.
   */
  static final class UnixCaret extends Node {

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int startIndex = matcher.from;
      int endIndex = matcher.to;
      if (!matcher.anchoringBounds) {
        startIndex = 0;
        endIndex = matcher.getTextLength();
      }
      // Perl does not match ^ at end of input even after newline
      if (i == endIndex) {
        matcher.hitEnd = true;
        return false;
      }
      if (i > startIndex) {
        char ch = seq.charAt(i - 1);
        if (ch != '\n') {
          return false;
        }
      }
      return next.match(matcher, i, seq);
    }
  }

  /**
   * Node to match the location where the last match ended.
   * This is used for the \G construct.
   */
  static final class LastMatch extends Node {

    boolean match(Matcher matcher, int i, CharSequence seq) {
      if (i != matcher.oldLast) {
        return false;
      }
      return next.match(matcher, i, seq);
    }
  }

  /**
   * Node to anchor at the end of a line or the end of input based on the
   * multiline mode.
   *
   * When not in multiline mode, the $ can only match at the very end
   * of the input, unless the input ends in a line terminator in which
   * it matches right before the last line terminator.
   *
   * Note that \r\n is considered an atomic line terminator.
   *
   * Like ^ the $ operator matches at a position, it does not match the
   * line terminators themselves.
   */
  static final class Dollar extends Node {

    boolean multiline;

    Dollar(boolean mul) {
      multiline = mul;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int endIndex = (matcher.anchoringBounds) ?
          matcher.to : matcher.getTextLength();
      if (!multiline) {
        if (i < endIndex - 2) {
          return false;
        }
        if (i == endIndex - 2) {
          char ch = seq.charAt(i);
          if (ch != '\r') {
            return false;
          }
          ch = seq.charAt(i + 1);
          if (ch != '\n') {
            return false;
          }
        }
      }
      // Matches before any line terminator; also matches at the
      // end of input
      // Before line terminator:
      // If multiline, we match here no matter what
      // If not multiline, fall through so that the end
      // is marked as hit; this must be a /r/n or a /n
      // at the very end so the end was hit; more input
      // could make this not match here
      if (i < endIndex) {
        char ch = seq.charAt(i);
        if (ch == '\n') {
          // No match between \r\n
          if (i > 0 && seq.charAt(i - 1) == '\r') {
            return false;
          }
          if (multiline) {
            return next.match(matcher, i, seq);
          }
        } else if (ch == '\r' || ch == '\u0085' ||
            (ch | 1) == '\u2029') {
          if (multiline) {
            return next.match(matcher, i, seq);
          }
        } else { // No line terminator, no match
          return false;
        }
      }
      // Matched at current end so hit end
      matcher.hitEnd = true;
      // If a $ matches because of end of input, then more input
      // could cause it to fail!
      matcher.requireEnd = true;
      return next.match(matcher, i, seq);
    }

    boolean study(TreeInfo info) {
      next.study(info);
      return info.deterministic;
    }
  }

  /**
   * Node to anchor at the end of a line or the end of input based on the
   * multiline mode when in unix lines mode.
   */
  static final class UnixDollar extends Node {

    boolean multiline;

    UnixDollar(boolean mul) {
      multiline = mul;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int endIndex = (matcher.anchoringBounds) ?
          matcher.to : matcher.getTextLength();
      if (i < endIndex) {
        char ch = seq.charAt(i);
        if (ch == '\n') {
          // If not multiline, then only possible to
          // match at very end or one before end
          if (multiline == false && i != endIndex - 1) {
            return false;
          }
          // If multiline return next.match without setting
          // matcher.hitEnd
          if (multiline) {
            return next.match(matcher, i, seq);
          }
        } else {
          return false;
        }
      }
      // Matching because at the end or 1 before the end;
      // more input could change this so set hitEnd
      matcher.hitEnd = true;
      // If a $ matches because of end of input, then more input
      // could cause it to fail!
      matcher.requireEnd = true;
      return next.match(matcher, i, seq);
    }

    boolean study(TreeInfo info) {
      next.study(info);
      return info.deterministic;
    }
  }

  /**
   * Node class that matches a Unicode line ending '\R'
   */
  static final class LineEnding extends Node {

    boolean match(Matcher matcher, int i, CharSequence seq) {
      // (u+000Du+000A|[u+000Au+000Bu+000Cu+000Du+0085u+2028u+2029])
      if (i < matcher.to) {
        int ch = seq.charAt(i);
        if (ch == 0x0A || ch == 0x0B || ch == 0x0C ||
            ch == 0x85 || ch == 0x2028 || ch == 0x2029) {
          return next.match(matcher, i + 1, seq);
        }
        if (ch == 0x0D) {
          i++;
          if (i < matcher.to && seq.charAt(i) == 0x0A) {
            i++;
          }
          return next.match(matcher, i, seq);
        }
      } else {
        matcher.hitEnd = true;
      }
      return false;
    }

    boolean study(TreeInfo info) {
      info.minLength++;
      info.maxLength += 2;
      return next.study(info);
    }
  }

  /**
   * Abstract node class to match one character satisfying some
   * boolean property.
   */
  private static abstract class CharProperty extends Node {

    abstract boolean isSatisfiedBy(int ch);

    CharProperty complement() {
      return new CharProperty() {
        boolean isSatisfiedBy(int ch) {
          return !CharProperty.this.isSatisfiedBy(ch);
        }
      };
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      if (i < matcher.to) {
        int ch = Character.codePointAt(seq, i);
        return isSatisfiedBy(ch)
            && next.match(matcher, i + Character.charCount(ch), seq);
      } else {
        matcher.hitEnd = true;
        return false;
      }
    }

    boolean study(TreeInfo info) {
      info.minLength++;
      info.maxLength++;
      return next.study(info);
    }
  }

  /**
   * Optimized version of CharProperty that works only for
   * properties never satisfied by Supplementary characters.
   */
  private static abstract class BmpCharProperty extends CharProperty {

    boolean match(Matcher matcher, int i, CharSequence seq) {
      if (i < matcher.to) {
        return isSatisfiedBy(seq.charAt(i))
            && next.match(matcher, i + 1, seq);
      } else {
        matcher.hitEnd = true;
        return false;
      }
    }
  }

  /**
   * Node class that matches a Supplementary Unicode character
   */
  static final class SingleS extends CharProperty {

    final int c;

    SingleS(int c) {
      this.c = c;
    }

    boolean isSatisfiedBy(int ch) {
      return ch == c;
    }
  }

  /**
   * Optimization -- matches a given BMP character
   */
  static final class Single extends BmpCharProperty {

    final int c;

    Single(int c) {
      this.c = c;
    }

    boolean isSatisfiedBy(int ch) {
      return ch == c;
    }
  }

  /**
   * Case insensitive matches a given BMP character
   */
  static final class SingleI extends BmpCharProperty {

    final int lower;
    final int upper;

    SingleI(int lower, int upper) {
      this.lower = lower;
      this.upper = upper;
    }

    boolean isSatisfiedBy(int ch) {
      return ch == lower || ch == upper;
    }
  }

  /**
   * Unicode case insensitive matches a given Unicode character
   */
  static final class SingleU extends CharProperty {

    final int lower;

    SingleU(int lower) {
      this.lower = lower;
    }

    boolean isSatisfiedBy(int ch) {
      return lower == ch ||
          lower == Character.toLowerCase(Character.toUpperCase(ch));
    }
  }

  /**
   * Node class that matches a Unicode block.
   */
  static final class Block extends CharProperty {

    final Character.UnicodeBlock block;

    Block(Character.UnicodeBlock block) {
      this.block = block;
    }

    boolean isSatisfiedBy(int ch) {
      return block == Character.UnicodeBlock.of(ch);
    }
  }

  /**
   * Node class that matches a Unicode script
   */
  static final class Script extends CharProperty {

    final Character.UnicodeScript script;

    Script(Character.UnicodeScript script) {
      this.script = script;
    }

    boolean isSatisfiedBy(int ch) {
      return script == Character.UnicodeScript.of(ch);
    }
  }

  /**
   * Node class that matches a Unicode category.
   */
  static final class Category extends CharProperty {

    final int typeMask;

    Category(int typeMask) {
      this.typeMask = typeMask;
    }

    boolean isSatisfiedBy(int ch) {
      return (typeMask & (1 << Character.getType(ch))) != 0;
    }
  }

  /**
   * Node class that matches a Unicode "type"
   */
  static final class Utype extends CharProperty {

    final UnicodeProp uprop;

    Utype(UnicodeProp uprop) {
      this.uprop = uprop;
    }

    boolean isSatisfiedBy(int ch) {
      return uprop.is(ch);
    }
  }

  /**
   * Node class that matches a POSIX type.
   */
  static final class Ctype extends BmpCharProperty {

    final int ctype;

    Ctype(int ctype) {
      this.ctype = ctype;
    }

    boolean isSatisfiedBy(int ch) {
      return ch < 128 && ASCII.isType(ch, ctype);
    }
  }

  /**
   * Node class that matches a Perl vertical whitespace
   */
  static final class VertWS extends BmpCharProperty {

    boolean isSatisfiedBy(int cp) {
      return (cp >= 0x0A && cp <= 0x0D) ||
          cp == 0x85 || cp == 0x2028 || cp == 0x2029;
    }
  }

  /**
   * Node class that matches a Perl horizontal whitespace
   */
  static final class HorizWS extends BmpCharProperty {

    boolean isSatisfiedBy(int cp) {
      return cp == 0x09 || cp == 0x20 || cp == 0xa0 ||
          cp == 0x1680 || cp == 0x180e ||
          cp >= 0x2000 && cp <= 0x200a ||
          cp == 0x202f || cp == 0x205f || cp == 0x3000;
    }
  }

  /**
   * Base class for all Slice nodes
   */
  static class SliceNode extends Node {

    int[] buffer;

    SliceNode(int[] buf) {
      buffer = buf;
    }

    boolean study(TreeInfo info) {
      info.minLength += buffer.length;
      info.maxLength += buffer.length;
      return next.study(info);
    }
  }

  /**
   * Node class for a case sensitive/BMP-only sequence of literal
   * characters.
   */
  static final class Slice extends SliceNode {

    Slice(int[] buf) {
      super(buf);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int[] buf = buffer;
      int len = buf.length;
      for (int j = 0; j < len; j++) {
        if ((i + j) >= matcher.to) {
          matcher.hitEnd = true;
          return false;
        }
        if (buf[j] != seq.charAt(i + j)) {
          return false;
        }
      }
      return next.match(matcher, i + len, seq);
    }
  }

  /**
   * Node class for a case_insensitive/BMP-only sequence of literal
   * characters.
   */
  static class SliceI extends SliceNode {

    SliceI(int[] buf) {
      super(buf);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int[] buf = buffer;
      int len = buf.length;
      for (int j = 0; j < len; j++) {
        if ((i + j) >= matcher.to) {
          matcher.hitEnd = true;
          return false;
        }
        int c = seq.charAt(i + j);
        if (buf[j] != c &&
            buf[j] != ASCII.toLower(c)) {
          return false;
        }
      }
      return next.match(matcher, i + len, seq);
    }
  }

  /**
   * Node class for a unicode_case_insensitive/BMP-only sequence of
   * literal characters. Uses unicode case folding.
   */
  static final class SliceU extends SliceNode {

    SliceU(int[] buf) {
      super(buf);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int[] buf = buffer;
      int len = buf.length;
      for (int j = 0; j < len; j++) {
        if ((i + j) >= matcher.to) {
          matcher.hitEnd = true;
          return false;
        }
        int c = seq.charAt(i + j);
        if (buf[j] != c &&
            buf[j] != Character.toLowerCase(Character.toUpperCase(c))) {
          return false;
        }
      }
      return next.match(matcher, i + len, seq);
    }
  }

  /**
   * Node class for a case sensitive sequence of literal characters
   * including supplementary characters.
   */
  static final class SliceS extends SliceNode {

    SliceS(int[] buf) {
      super(buf);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int[] buf = buffer;
      int x = i;
      for (int j = 0; j < buf.length; j++) {
        if (x >= matcher.to) {
          matcher.hitEnd = true;
          return false;
        }
        int c = Character.codePointAt(seq, x);
        if (buf[j] != c) {
          return false;
        }
        x += Character.charCount(c);
        if (x > matcher.to) {
          matcher.hitEnd = true;
          return false;
        }
      }
      return next.match(matcher, x, seq);
    }
  }

  /**
   * Node class for a case insensitive sequence of literal characters
   * including supplementary characters.
   */
  static class SliceIS extends SliceNode {

    SliceIS(int[] buf) {
      super(buf);
    }

    int toLower(int c) {
      return ASCII.toLower(c);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int[] buf = buffer;
      int x = i;
      for (int j = 0; j < buf.length; j++) {
        if (x >= matcher.to) {
          matcher.hitEnd = true;
          return false;
        }
        int c = Character.codePointAt(seq, x);
        if (buf[j] != c && buf[j] != toLower(c)) {
          return false;
        }
        x += Character.charCount(c);
        if (x > matcher.to) {
          matcher.hitEnd = true;
          return false;
        }
      }
      return next.match(matcher, x, seq);
    }
  }

  /**
   * Node class for a case insensitive sequence of literal characters.
   * Uses unicode case folding.
   */
  static final class SliceUS extends SliceIS {

    SliceUS(int[] buf) {
      super(buf);
    }

    int toLower(int c) {
      return Character.toLowerCase(Character.toUpperCase(c));
    }
  }

  private static boolean inRange(int lower, int ch, int upper) {
    return lower <= ch && ch <= upper;
  }

  /**
   * Returns node for matching characters within an explicit value range.
   */
  private static CharProperty rangeFor(final int lower,
      final int upper) {
    return new CharProperty() {
      boolean isSatisfiedBy(int ch) {
        return inRange(lower, ch, upper);
      }
    };
  }

  /**
   * Returns node for matching characters within an explicit value
   * range in a case insensitive manner.
   */
  private CharProperty caseInsensitiveRangeFor(final int lower,
      final int upper) {
    if (has(UNICODE_CASE)) {
      return new CharProperty() {
        boolean isSatisfiedBy(int ch) {
          if (inRange(lower, ch, upper)) {
            return true;
          }
          int up = Character.toUpperCase(ch);
          return inRange(lower, up, upper) ||
              inRange(lower, Character.toLowerCase(up), upper);
        }
      };
    }
    return new CharProperty() {
      boolean isSatisfiedBy(int ch) {
        return inRange(lower, ch, upper) ||
            ASCII.isAscii(ch) &&
                (inRange(lower, ASCII.toUpper(ch), upper) ||
                    inRange(lower, ASCII.toLower(ch), upper));
      }
    };
  }

  /**
   * Implements the Unicode category ALL and the dot metacharacter when
   * in dotall mode.
   */
  static final class All extends CharProperty {

    boolean isSatisfiedBy(int ch) {
      return true;
    }
  }

  /**
   * Node class for the dot metacharacter when dotall is not enabled.
   */
  static final class Dot extends CharProperty {

    boolean isSatisfiedBy(int ch) {
      return (ch != '\n' && ch != '\r'
          && (ch | 1) != '\u2029'
          && ch != '\u0085');
    }
  }

  /**
   * Node class for the dot metacharacter when dotall is not enabled
   * but UNIX_LINES is enabled.
   */
  static final class UnixDot extends CharProperty {

    boolean isSatisfiedBy(int ch) {
      return ch != '\n';
    }
  }

  /**
   * The 0 or 1 quantifier. This one class implements all three types.
   */
  static final class Ques extends Node {

    Node atom;
    int type;

    Ques(Node node, int type) {
      this.atom = node;
      this.type = type;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      switch (type) {
        case GREEDY:
          return (atom.match(matcher, i, seq) && next.match(matcher, matcher.last, seq))
              || next.match(matcher, i, seq);
        case LAZY:
          return next.match(matcher, i, seq)
              || (atom.match(matcher, i, seq) && next.match(matcher, matcher.last, seq));
        case POSSESSIVE:
          if (atom.match(matcher, i, seq)) {
            i = matcher.last;
          }
          return next.match(matcher, i, seq);
        default:
          return atom.match(matcher, i, seq) && next.match(matcher, matcher.last, seq);
      }
    }

    boolean study(TreeInfo info) {
      if (type != INDEPENDENT) {
        int minL = info.minLength;
        atom.study(info);
        info.minLength = minL;
        info.deterministic = false;
        return next.study(info);
      } else {
        atom.study(info);
        return next.study(info);
      }
    }
  }

  /**
   * Handles the curly-brace style repetition with a specified minimum and
   * maximum occurrences. The * quantifier is handled as a special case.
   * This class handles the three types.
   */
  static final class Curly extends Node {

    Node atom;
    int type;
    int cmin;
    int cmax;

    Curly(Node node, int cmin, int cmax, int type) {
      this.atom = node;
      this.type = type;
      this.cmin = cmin;
      this.cmax = cmax;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int j;
      for (j = 0; j < cmin; j++) {
        if (atom.match(matcher, i, seq)) {
          i = matcher.last;
          continue;
        }
        return false;
      }
      if (type == GREEDY) {
        return match0(matcher, i, j, seq);
      } else if (type == LAZY) {
        return match1(matcher, i, j, seq);
      } else {
        return match2(matcher, i, j, seq);
      }
    }

    // Greedy match.
    // i is the index to start matching at
    // j is the number of atoms that have matched
    boolean match0(Matcher matcher, int i, int j, CharSequence seq) {
      if (j >= cmax) {
        // We have matched the maximum... continue with the rest of
        // the regular expression
        return next.match(matcher, i, seq);
      }
      int backLimit = j;
      while (atom.match(matcher, i, seq)) {
        // k is the length of this match
        int k = matcher.last - i;
        if (k == 0) // Zero length match
        {
          break;
        }
        // Move up index and number matched
        i = matcher.last;
        j++;
        // We are greedy so match as many as we can
        while (j < cmax) {
          if (!atom.match(matcher, i, seq)) {
            break;
          }
          if (i + k != matcher.last) {
            if (match0(matcher, matcher.last, j + 1, seq)) {
              return true;
            }
            break;
          }
          i += k;
          j++;
        }
        // Handle backing off if match fails
        while (j >= backLimit) {
          if (next.match(matcher, i, seq)) {
            return true;
          }
          i -= k;
          j--;
        }
        return false;
      }
      return next.match(matcher, i, seq);
    }

    // Reluctant match. At this point, the minimum has been satisfied.
    // i is the index to start matching at
    // j is the number of atoms that have matched
    boolean match1(Matcher matcher, int i, int j, CharSequence seq) {
      for (; ; ) {
        // Try finishing match without consuming any more
        if (next.match(matcher, i, seq)) {
          return true;
        }
        // At the maximum, no match found
        if (j >= cmax) {
          return false;
        }
        // Okay, must try one more atom
        if (!atom.match(matcher, i, seq)) {
          return false;
        }
        // If we haven't moved forward then must break out
        if (i == matcher.last) {
          return false;
        }
        // Move up index and number matched
        i = matcher.last;
        j++;
      }
    }

    boolean match2(Matcher matcher, int i, int j, CharSequence seq) {
      for (; j < cmax; j++) {
        if (!atom.match(matcher, i, seq)) {
          break;
        }
        if (i == matcher.last) {
          break;
        }
        i = matcher.last;
      }
      return next.match(matcher, i, seq);
    }

    boolean study(TreeInfo info) {
      // Save original info
      int minL = info.minLength;
      int maxL = info.maxLength;
      boolean maxV = info.maxValid;
      boolean detm = info.deterministic;
      info.reset();

      atom.study(info);

      int temp = info.minLength * cmin + minL;
      if (temp < minL) {
        temp = 0xFFFFFFF; // arbitrary large number
      }
      info.minLength = temp;

      if (maxV & info.maxValid) {
        temp = info.maxLength * cmax + maxL;
        info.maxLength = temp;
        if (temp < maxL) {
          info.maxValid = false;
        }
      } else {
        info.maxValid = false;
      }

      if (info.deterministic && cmin == cmax) {
        info.deterministic = detm;
      } else {
        info.deterministic = false;
      }
      return next.study(info);
    }
  }

  /**
   * Handles the curly-brace style repetition with a specified minimum and
   * maximum occurrences in deterministic cases. This is an iterative
   * optimization over the Prolog and Loop system which would handle this
   * in a recursive way. The * quantifier is handled as a special case.
   * If capture is true then this class saves group settings and ensures
   * that groups are unset when backing off of a group match.
   */
  static final class GroupCurly extends Node {

    Node atom;
    int type;
    int cmin;
    int cmax;
    int localIndex;
    int groupIndex;
    boolean capture;

    GroupCurly(Node node, int cmin, int cmax, int type, int local,
        int group, boolean capture) {
      this.atom = node;
      this.type = type;
      this.cmin = cmin;
      this.cmax = cmax;
      this.localIndex = local;
      this.groupIndex = group;
      this.capture = capture;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int[] groups = matcher.groups;
      int[] locals = matcher.locals;
      int save0 = locals[localIndex];
      int save1 = 0;
      int save2 = 0;

      if (capture) {
        save1 = groups[groupIndex];
        save2 = groups[groupIndex + 1];
      }

      // Notify GroupTail there is no need to setup group info
      // because it will be set here
      locals[localIndex] = -1;

      boolean ret = true;
      for (int j = 0; j < cmin; j++) {
        if (atom.match(matcher, i, seq)) {
          if (capture) {
            groups[groupIndex] = i;
            groups[groupIndex + 1] = matcher.last;
          }
          i = matcher.last;
        } else {
          ret = false;
          break;
        }
      }
      if (ret) {
        if (type == GREEDY) {
          ret = match0(matcher, i, cmin, seq);
        } else if (type == LAZY) {
          ret = match1(matcher, i, cmin, seq);
        } else {
          ret = match2(matcher, i, cmin, seq);
        }
      }
      if (!ret) {
        locals[localIndex] = save0;
        if (capture) {
          groups[groupIndex] = save1;
          groups[groupIndex + 1] = save2;
        }
      }
      return ret;
    }

    // Aggressive group match
    boolean match0(Matcher matcher, int i, int j, CharSequence seq) {
      // don't back off passing the starting "j"
      int min = j;
      int[] groups = matcher.groups;
      int save0 = 0;
      int save1 = 0;
      if (capture) {
        save0 = groups[groupIndex];
        save1 = groups[groupIndex + 1];
      }
      for (; ; ) {
        if (j >= cmax) {
          break;
        }
        if (!atom.match(matcher, i, seq)) {
          break;
        }
        int k = matcher.last - i;
        if (k <= 0) {
          if (capture) {
            groups[groupIndex] = i;
            groups[groupIndex + 1] = i + k;
          }
          i = i + k;
          break;
        }
        for (; ; ) {
          if (capture) {
            groups[groupIndex] = i;
            groups[groupIndex + 1] = i + k;
          }
          i = i + k;
          if (++j >= cmax) {
            break;
          }
          if (!atom.match(matcher, i, seq)) {
            break;
          }
          if (i + k != matcher.last) {
            if (match0(matcher, i, j, seq)) {
              return true;
            }
            break;
          }
        }
        while (j > min) {
          if (next.match(matcher, i, seq)) {
            if (capture) {
              groups[groupIndex + 1] = i;
              groups[groupIndex] = i - k;
            }
            return true;
          }
          // backing off
          i = i - k;
          if (capture) {
            groups[groupIndex + 1] = i;
            groups[groupIndex] = i - k;
          }
          j--;

        }
        break;
      }
      if (capture) {
        groups[groupIndex] = save0;
        groups[groupIndex + 1] = save1;
      }
      return next.match(matcher, i, seq);
    }

    // Reluctant matching
    boolean match1(Matcher matcher, int i, int j, CharSequence seq) {
      for (; ; ) {
        if (next.match(matcher, i, seq)) {
          return true;
        }
        if (j >= cmax) {
          return false;
        }
        if (!atom.match(matcher, i, seq)) {
          return false;
        }
        if (i == matcher.last) {
          return false;
        }
        if (capture) {
          matcher.groups[groupIndex] = i;
          matcher.groups[groupIndex + 1] = matcher.last;
        }
        i = matcher.last;
        j++;
      }
    }

    // Possessive matching
    boolean match2(Matcher matcher, int i, int j, CharSequence seq) {
      for (; j < cmax; j++) {
        if (!atom.match(matcher, i, seq)) {
          break;
        }
        if (capture) {
          matcher.groups[groupIndex] = i;
          matcher.groups[groupIndex + 1] = matcher.last;
        }
        if (i == matcher.last) {
          break;
        }
        i = matcher.last;
      }
      return next.match(matcher, i, seq);
    }

    boolean study(TreeInfo info) {
      // Save original info
      int minL = info.minLength;
      int maxL = info.maxLength;
      boolean maxV = info.maxValid;
      boolean detm = info.deterministic;
      info.reset();

      atom.study(info);

      int temp = info.minLength * cmin + minL;
      if (temp < minL) {
        temp = 0xFFFFFFF; // Arbitrary large number
      }
      info.minLength = temp;

      if (maxV & info.maxValid) {
        temp = info.maxLength * cmax + maxL;
        info.maxLength = temp;
        if (temp < maxL) {
          info.maxValid = false;
        }
      } else {
        info.maxValid = false;
      }

      if (info.deterministic && cmin == cmax) {
        info.deterministic = detm;
      } else {
        info.deterministic = false;
      }
      return next.study(info);
    }
  }

  /**
   * A Guard node at the end of each atom node in a Branch. It
   * serves the purpose of chaining the "match" operation to
   * "next" but not the "study", so we can collect the TreeInfo
   * of each atom node without including the TreeInfo of the
   * "next".
   */
  static final class BranchConn extends Node {

    BranchConn() {
    }

    ;

    boolean match(Matcher matcher, int i, CharSequence seq) {
      return next.match(matcher, i, seq);
    }

    boolean study(TreeInfo info) {
      return info.deterministic;
    }
  }

  /**
   * Handles the branching of alternations. Note this is also used for
   * the ? quantifier to branch between the case where it matches once
   * and where it does not occur.
   */
  static final class Branch extends Node {

    Node[] atoms = new Node[2];
    int size = 2;
    Node conn;

    Branch(Node first, Node second, Node branchConn) {
      conn = branchConn;
      atoms[0] = first;
      atoms[1] = second;
    }

    void add(Node node) {
      if (size >= atoms.length) {
        Node[] tmp = new Node[atoms.length * 2];
        System.arraycopy(atoms, 0, tmp, 0, atoms.length);
        atoms = tmp;
      }
      atoms[size++] = node;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      for (int n = 0; n < size; n++) {
        if (atoms[n] == null) {
          if (conn.next.match(matcher, i, seq)) {
            return true;
          }
        } else if (atoms[n].match(matcher, i, seq)) {
          return true;
        }
      }
      return false;
    }

    boolean study(TreeInfo info) {
      int minL = info.minLength;
      int maxL = info.maxLength;
      boolean maxV = info.maxValid;

      int minL2 = Integer.MAX_VALUE; //arbitrary large enough num
      int maxL2 = -1;
      for (int n = 0; n < size; n++) {
        info.reset();
        if (atoms[n] != null) {
          atoms[n].study(info);
        }
        minL2 = Math.min(minL2, info.minLength);
        maxL2 = Math.max(maxL2, info.maxLength);
        maxV = (maxV & info.maxValid);
      }

      minL += minL2;
      maxL += maxL2;

      info.reset();
      conn.next.study(info);

      info.minLength += minL;
      info.maxLength += maxL;
      info.maxValid &= maxV;
      info.deterministic = false;
      return false;
    }
  }

  /**
   * The GroupHead saves the location where the group begins in the locals
   * and restores them when the match is done.
   *
   * The matchRef is used when a reference to this group is accessed later
   * in the expression. The locals will have a negative value in them to
   * indicate that we do not want to unset the group if the reference
   * doesn't match.
   */
  static final class GroupHead extends Node {

    int localIndex;

    GroupHead(int localCount) {
      localIndex = localCount;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int save = matcher.locals[localIndex];
      matcher.locals[localIndex] = i;
      boolean ret = next.match(matcher, i, seq);
      matcher.locals[localIndex] = save;
      return ret;
    }

    boolean matchRef(Matcher matcher, int i, CharSequence seq) {
      int save = matcher.locals[localIndex];
      matcher.locals[localIndex] = ~i; // HACK
      boolean ret = next.match(matcher, i, seq);
      matcher.locals[localIndex] = save;
      return ret;
    }
  }

  /**
   * Recursive reference to a group in the regular expression. It calls
   * matchRef because if the reference fails to match we would not unset
   * the group.
   */
  static final class GroupRef extends Node {

    GroupHead head;

    GroupRef(GroupHead head) {
      this.head = head;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      return head.matchRef(matcher, i, seq)
          && next.match(matcher, matcher.last, seq);
    }

    boolean study(TreeInfo info) {
      info.maxValid = false;
      info.deterministic = false;
      return next.study(info);
    }
  }

  /**
   * The GroupTail handles the setting of group beginning and ending
   * locations when groups are successfully matched. It must also be able to
   * unset groups that have to be backed off of.
   *
   * The GroupTail node is also used when a previous group is referenced,
   * and in that case no group information needs to be set.
   */
  static final class GroupTail extends Node {

    int localIndex;
    int groupIndex;

    GroupTail(int localCount, int groupCount) {
      localIndex = localCount;
      groupIndex = groupCount + groupCount;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int tmp = matcher.locals[localIndex];
      if (tmp >= 0) { // This is the normal group case.
        // Save the group so we can unset it if it
        // backs off of a match.
        int groupStart = matcher.groups[groupIndex];
        int groupEnd = matcher.groups[groupIndex + 1];

        matcher.groups[groupIndex] = tmp;
        matcher.groups[groupIndex + 1] = i;
        if (next.match(matcher, i, seq)) {
          return true;
        }
        matcher.groups[groupIndex] = groupStart;
        matcher.groups[groupIndex + 1] = groupEnd;
        return false;
      } else {
        // This is a group reference case. We don't need to save any
        // group info because it isn't really a group.
        matcher.last = i;
        return true;
      }
    }
  }

  /**
   * This sets up a loop to handle a recursive quantifier structure.
   */
  static final class Prolog extends Node {

    Loop loop;

    Prolog(Loop loop) {
      this.loop = loop;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      return loop.matchInit(matcher, i, seq);
    }

    boolean study(TreeInfo info) {
      return loop.study(info);
    }
  }

  /**
   * Handles the repetition count for a greedy Curly. The matchInit
   * is called from the Prolog to save the index of where the group
   * beginning is stored. A zero length group check occurs in the
   * normal match but is skipped in the matchInit.
   */
  static class Loop extends Node {

    Node body;
    int countIndex; // local count index in matcher locals
    int beginIndex; // group beginning index
    int cmin, cmax;

    Loop(int countIndex, int beginIndex) {
      this.countIndex = countIndex;
      this.beginIndex = beginIndex;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      // Avoid infinite loop in zero-length case.
      if (i > matcher.locals[beginIndex]) {
        int count = matcher.locals[countIndex];

        // This block is for before we reach the minimum
        // iterations required for the loop to match
        if (count < cmin) {
          matcher.locals[countIndex] = count + 1;
          boolean b = body.match(matcher, i, seq);
          // If match failed we must backtrack, so
          // the loop count should NOT be incremented
          if (!b) {
            matcher.locals[countIndex] = count;
          }
          // Return success or failure since we are under
          // minimum
          return b;
        }
        // This block is for after we have the minimum
        // iterations required for the loop to match
        if (count < cmax) {
          matcher.locals[countIndex] = count + 1;
          boolean b = body.match(matcher, i, seq);
          // If match failed we must backtrack, so
          // the loop count should NOT be incremented
          if (!b) {
            matcher.locals[countIndex] = count;
          } else {
            return true;
          }
        }
      }
      return next.match(matcher, i, seq);
    }

    boolean matchInit(Matcher matcher, int i, CharSequence seq) {
      int save = matcher.locals[countIndex];
      boolean ret = false;
      if (0 < cmin) {
        matcher.locals[countIndex] = 1;
        ret = body.match(matcher, i, seq);
      } else if (0 < cmax) {
        matcher.locals[countIndex] = 1;
        ret = body.match(matcher, i, seq);
        if (ret == false) {
          ret = next.match(matcher, i, seq);
        }
      } else {
        ret = next.match(matcher, i, seq);
      }
      matcher.locals[countIndex] = save;
      return ret;
    }

    boolean study(TreeInfo info) {
      info.maxValid = false;
      info.deterministic = false;
      return false;
    }
  }

  /**
   * Handles the repetition count for a reluctant Curly. The matchInit
   * is called from the Prolog to save the index of where the group
   * beginning is stored. A zero length group check occurs in the
   * normal match but is skipped in the matchInit.
   */
  static final class LazyLoop extends Loop {

    LazyLoop(int countIndex, int beginIndex) {
      super(countIndex, beginIndex);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      // Check for zero length group
      if (i > matcher.locals[beginIndex]) {
        int count = matcher.locals[countIndex];
        if (count < cmin) {
          matcher.locals[countIndex] = count + 1;
          boolean result = body.match(matcher, i, seq);
          // If match failed we must backtrack, so
          // the loop count should NOT be incremented
          if (!result) {
            matcher.locals[countIndex] = count;
          }
          return result;
        }
        if (next.match(matcher, i, seq)) {
          return true;
        }
        if (count < cmax) {
          matcher.locals[countIndex] = count + 1;
          boolean result = body.match(matcher, i, seq);
          // If match failed we must backtrack, so
          // the loop count should NOT be incremented
          if (!result) {
            matcher.locals[countIndex] = count;
          }
          return result;
        }
        return false;
      }
      return next.match(matcher, i, seq);
    }

    boolean matchInit(Matcher matcher, int i, CharSequence seq) {
      int save = matcher.locals[countIndex];
      boolean ret = false;
      if (0 < cmin) {
        matcher.locals[countIndex] = 1;
        ret = body.match(matcher, i, seq);
      } else if (next.match(matcher, i, seq)) {
        ret = true;
      } else if (0 < cmax) {
        matcher.locals[countIndex] = 1;
        ret = body.match(matcher, i, seq);
      }
      matcher.locals[countIndex] = save;
      return ret;
    }

    boolean study(TreeInfo info) {
      info.maxValid = false;
      info.deterministic = false;
      return false;
    }
  }

  /**
   * Refers to a group in the regular expression. Attempts to match
   * whatever the group referred to last matched.
   */
  static class BackRef extends Node {

    int groupIndex;

    BackRef(int groupCount) {
      super();
      groupIndex = groupCount + groupCount;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int j = matcher.groups[groupIndex];
      int k = matcher.groups[groupIndex + 1];

      int groupSize = k - j;
      // If the referenced group didn't match, neither can this
      if (j < 0) {
        return false;
      }

      // If there isn't enough input left no match
      if (i + groupSize > matcher.to) {
        matcher.hitEnd = true;
        return false;
      }
      // Check each new char to make sure it matches what the group
      // referenced matched last time around
      for (int index = 0; index < groupSize; index++) {
        if (seq.charAt(i + index) != seq.charAt(j + index)) {
          return false;
        }
      }

      return next.match(matcher, i + groupSize, seq);
    }

    boolean study(TreeInfo info) {
      info.maxValid = false;
      return next.study(info);
    }
  }

  static class CIBackRef extends Node {

    int groupIndex;
    boolean doUnicodeCase;

    CIBackRef(int groupCount, boolean doUnicodeCase) {
      super();
      groupIndex = groupCount + groupCount;
      this.doUnicodeCase = doUnicodeCase;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int j = matcher.groups[groupIndex];
      int k = matcher.groups[groupIndex + 1];

      int groupSize = k - j;

      // If the referenced group didn't match, neither can this
      if (j < 0) {
        return false;
      }

      // If there isn't enough input left no match
      if (i + groupSize > matcher.to) {
        matcher.hitEnd = true;
        return false;
      }

      // Check each new char to make sure it matches what the group
      // referenced matched last time around
      int x = i;
      for (int index = 0; index < groupSize; index++) {
        int c1 = Character.codePointAt(seq, x);
        int c2 = Character.codePointAt(seq, j);
        if (c1 != c2) {
          if (doUnicodeCase) {
            int cc1 = Character.toUpperCase(c1);
            int cc2 = Character.toUpperCase(c2);
            if (cc1 != cc2 &&
                Character.toLowerCase(cc1) !=
                    Character.toLowerCase(cc2)) {
              return false;
            }
          } else {
            if (ASCII.toLower(c1) != ASCII.toLower(c2)) {
              return false;
            }
          }
        }
        x += Character.charCount(c1);
        j += Character.charCount(c2);
      }

      return next.match(matcher, i + groupSize, seq);
    }

    boolean study(TreeInfo info) {
      info.maxValid = false;
      return next.study(info);
    }
  }

  /**
   * Searches until the next instance of its atom. This is useful for
   * finding the atom efficiently without passing an instance of it
   * (greedy problem) and without a lot of wasted search time (reluctant
   * problem).
   */
  static final class First extends Node {

    Node atom;

    First(Node node) {
      this.atom = BnM.optimize(node);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      if (atom instanceof BnM) {
        return atom.match(matcher, i, seq)
            && next.match(matcher, matcher.last, seq);
      }
      for (; ; ) {
        if (i > matcher.to) {
          matcher.hitEnd = true;
          return false;
        }
        if (atom.match(matcher, i, seq)) {
          return next.match(matcher, matcher.last, seq);
        }
        i += countChars(seq, i, 1);
        matcher.first++;
      }
    }

    boolean study(TreeInfo info) {
      atom.study(info);
      info.maxValid = false;
      info.deterministic = false;
      return next.study(info);
    }
  }

  static final class Conditional extends Node {

    Node cond, yes, not;

    Conditional(Node cond, Node yes, Node not) {
      this.cond = cond;
      this.yes = yes;
      this.not = not;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      if (cond.match(matcher, i, seq)) {
        return yes.match(matcher, i, seq);
      } else {
        return not.match(matcher, i, seq);
      }
    }

    boolean study(TreeInfo info) {
      int minL = info.minLength;
      int maxL = info.maxLength;
      boolean maxV = info.maxValid;
      info.reset();
      yes.study(info);

      int minL2 = info.minLength;
      int maxL2 = info.maxLength;
      boolean maxV2 = info.maxValid;
      info.reset();
      not.study(info);

      info.minLength = minL + Math.min(minL2, info.minLength);
      info.maxLength = maxL + Math.max(maxL2, info.maxLength);
      info.maxValid = (maxV & maxV2 & info.maxValid);
      info.deterministic = false;
      return next.study(info);
    }
  }

  /**
   * Zero width positive lookahead.
   */
  static final class Pos extends Node {

    Node cond;

    Pos(Node cond) {
      this.cond = cond;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int savedTo = matcher.to;
      boolean conditionMatched = false;

      // Relax transparent region boundaries for lookahead
      if (matcher.transparentBounds) {
        matcher.to = matcher.getTextLength();
      }
      try {
        conditionMatched = cond.match(matcher, i, seq);
      } finally {
        // Reinstate region boundaries
        matcher.to = savedTo;
      }
      return conditionMatched && next.match(matcher, i, seq);
    }
  }

  /**
   * Zero width negative lookahead.
   */
  static final class Neg extends Node {

    Node cond;

    Neg(Node cond) {
      this.cond = cond;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int savedTo = matcher.to;
      boolean conditionMatched = false;

      // Relax transparent region boundaries for lookahead
      if (matcher.transparentBounds) {
        matcher.to = matcher.getTextLength();
      }
      try {
        if (i < matcher.to) {
          conditionMatched = !cond.match(matcher, i, seq);
        } else {
          // If a negative lookahead succeeds then more input
          // could cause it to fail!
          matcher.requireEnd = true;
          conditionMatched = !cond.match(matcher, i, seq);
        }
      } finally {
        // Reinstate region boundaries
        matcher.to = savedTo;
      }
      return conditionMatched && next.match(matcher, i, seq);
    }
  }

  /**
   * For use with lookbehinds; matches the position where the lookbehind
   * was encountered.
   */
  static Node lookbehindEnd = new Node() {
    boolean match(Matcher matcher, int i, CharSequence seq) {
      return i == matcher.lookbehindTo;
    }
  };

  /**
   * Zero width positive lookbehind.
   */
  static class Behind extends Node {

    Node cond;
    int rmax, rmin;

    Behind(Node cond, int rmax, int rmin) {
      this.cond = cond;
      this.rmax = rmax;
      this.rmin = rmin;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int savedFrom = matcher.from;
      boolean conditionMatched = false;
      int startIndex = (!matcher.transparentBounds) ?
          matcher.from : 0;
      int from = Math.max(i - rmax, startIndex);
      // Set end boundary
      int savedLBT = matcher.lookbehindTo;
      matcher.lookbehindTo = i;
      // Relax transparent region boundaries for lookbehind
      if (matcher.transparentBounds) {
        matcher.from = 0;
      }
      for (int j = i - rmin; !conditionMatched && j >= from; j--) {
        conditionMatched = cond.match(matcher, j, seq);
      }
      matcher.from = savedFrom;
      matcher.lookbehindTo = savedLBT;
      return conditionMatched && next.match(matcher, i, seq);
    }
  }

  /**
   * Zero width positive lookbehind, including supplementary
   * characters or unpaired surrogates.
   */
  static final class BehindS extends Behind {

    BehindS(Node cond, int rmax, int rmin) {
      super(cond, rmax, rmin);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int rmaxChars = countChars(seq, i, -rmax);
      int rminChars = countChars(seq, i, -rmin);
      int savedFrom = matcher.from;
      int startIndex = (!matcher.transparentBounds) ?
          matcher.from : 0;
      boolean conditionMatched = false;
      int from = Math.max(i - rmaxChars, startIndex);
      // Set end boundary
      int savedLBT = matcher.lookbehindTo;
      matcher.lookbehindTo = i;
      // Relax transparent region boundaries for lookbehind
      if (matcher.transparentBounds) {
        matcher.from = 0;
      }

      for (int j = i - rminChars;
          !conditionMatched && j >= from;
          j -= j > from ? countChars(seq, j, -1) : 1) {
        conditionMatched = cond.match(matcher, j, seq);
      }
      matcher.from = savedFrom;
      matcher.lookbehindTo = savedLBT;
      return conditionMatched && next.match(matcher, i, seq);
    }
  }

  /**
   * Zero width negative lookbehind.
   */
  static class NotBehind extends Node {

    Node cond;
    int rmax, rmin;

    NotBehind(Node cond, int rmax, int rmin) {
      this.cond = cond;
      this.rmax = rmax;
      this.rmin = rmin;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int savedLBT = matcher.lookbehindTo;
      int savedFrom = matcher.from;
      boolean conditionMatched = false;
      int startIndex = (!matcher.transparentBounds) ?
          matcher.from : 0;
      int from = Math.max(i - rmax, startIndex);
      matcher.lookbehindTo = i;
      // Relax transparent region boundaries for lookbehind
      if (matcher.transparentBounds) {
        matcher.from = 0;
      }
      for (int j = i - rmin; !conditionMatched && j >= from; j--) {
        conditionMatched = cond.match(matcher, j, seq);
      }
      // Reinstate region boundaries
      matcher.from = savedFrom;
      matcher.lookbehindTo = savedLBT;
      return !conditionMatched && next.match(matcher, i, seq);
    }
  }

  /**
   * Zero width negative lookbehind, including supplementary
   * characters or unpaired surrogates.
   */
  static final class NotBehindS extends NotBehind {

    NotBehindS(Node cond, int rmax, int rmin) {
      super(cond, rmax, rmin);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int rmaxChars = countChars(seq, i, -rmax);
      int rminChars = countChars(seq, i, -rmin);
      int savedFrom = matcher.from;
      int savedLBT = matcher.lookbehindTo;
      boolean conditionMatched = false;
      int startIndex = (!matcher.transparentBounds) ?
          matcher.from : 0;
      int from = Math.max(i - rmaxChars, startIndex);
      matcher.lookbehindTo = i;
      // Relax transparent region boundaries for lookbehind
      if (matcher.transparentBounds) {
        matcher.from = 0;
      }
      for (int j = i - rminChars;
          !conditionMatched && j >= from;
          j -= j > from ? countChars(seq, j, -1) : 1) {
        conditionMatched = cond.match(matcher, j, seq);
      }
      //Reinstate region boundaries
      matcher.from = savedFrom;
      matcher.lookbehindTo = savedLBT;
      return !conditionMatched && next.match(matcher, i, seq);
    }
  }

  /**
   * Returns the set union of two CharProperty nodes.
   */
  private static CharProperty union(final CharProperty lhs,
      final CharProperty rhs) {
    return new CharProperty() {
      boolean isSatisfiedBy(int ch) {
        return lhs.isSatisfiedBy(ch) || rhs.isSatisfiedBy(ch);
      }
    };
  }

  /**
   * Returns the set intersection of two CharProperty nodes.
   */
  private static CharProperty intersection(final CharProperty lhs,
      final CharProperty rhs) {
    return new CharProperty() {
      boolean isSatisfiedBy(int ch) {
        return lhs.isSatisfiedBy(ch) && rhs.isSatisfiedBy(ch);
      }
    };
  }

  /**
   * Returns the set difference of two CharProperty nodes.
   */
  private static CharProperty setDifference(final CharProperty lhs,
      final CharProperty rhs) {
    return new CharProperty() {
      boolean isSatisfiedBy(int ch) {
        return !rhs.isSatisfiedBy(ch) && lhs.isSatisfiedBy(ch);
      }
    };
  }

  /**
   * Handles word boundaries. Includes a field to allow this one class to
   * deal with the different types of word boundaries we can match. The word
   * characters include underscores, letters, and digits. Non spacing marks
   * can are also part of a word if they have a base character, otherwise
   * they are ignored for purposes of finding word boundaries.
   */
  static final class Bound extends Node {

    static int LEFT = 0x1;
    static int RIGHT = 0x2;
    static int BOTH = 0x3;
    static int NONE = 0x4;
    int type;
    boolean useUWORD;

    Bound(int n, boolean useUWORD) {
      type = n;
      this.useUWORD = useUWORD;
    }

    boolean isWord(int ch) {
      return useUWORD ? UnicodeProp.WORD.is(ch)
          : (ch == '_' || Character.isLetterOrDigit(ch));
    }

    int check(Matcher matcher, int i, CharSequence seq) {
      int ch;
      boolean left = false;
      int startIndex = matcher.from;
      int endIndex = matcher.to;
      if (matcher.transparentBounds) {
        startIndex = 0;
        endIndex = matcher.getTextLength();
      }
      if (i > startIndex) {
        ch = Character.codePointBefore(seq, i);
        left = (isWord(ch) ||
            ((Character.getType(ch) == Character.NON_SPACING_MARK)
                && hasBaseCharacter(matcher, i - 1, seq)));
      }
      boolean right = false;
      if (i < endIndex) {
        ch = Character.codePointAt(seq, i);
        right = (isWord(ch) ||
            ((Character.getType(ch) == Character.NON_SPACING_MARK)
                && hasBaseCharacter(matcher, i, seq)));
      } else {
        // Tried to access char past the end
        matcher.hitEnd = true;
        // The addition of another char could wreck a boundary
        matcher.requireEnd = true;
      }
      return ((left ^ right) ? (right ? LEFT : RIGHT) : NONE);
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      return (check(matcher, i, seq) & type) > 0
          && next.match(matcher, i, seq);
    }
  }

  /**
   * Non spacing marks only count as word characters in bounds calculations
   * if they have a base character.
   */
  private static boolean hasBaseCharacter(Matcher matcher, int i,
      CharSequence seq) {
    int start = (!matcher.transparentBounds) ?
        matcher.from : 0;
    for (int x = i; x >= start; x--) {
      int ch = Character.codePointAt(seq, x);
      if (Character.isLetterOrDigit(ch)) {
        return true;
      }
      if (Character.getType(ch) == Character.NON_SPACING_MARK) {
        continue;
      }
      return false;
    }
    return false;
  }

  /**
   * Attempts to match a slice in the input using the Boyer-Moore string
   * matching algorithm. The algorithm is based on the idea that the
   * pattern can be shifted farther ahead in the search text if it is
   * matched right to left.
   * <p>
   * The pattern is compared to the input one character at a time, from
   * the rightmost character in the pattern to the left. If the characters
   * all match the pattern has been found. If a character does not match,
   * the pattern is shifted right a distance that is the maximum of two
   * functions, the bad character shift and the good suffix shift. This
   * shift moves the attempted match position through the input more
   * quickly than a naive one position at a time check.
   * <p>
   * The bad character shift is based on the character from the text that
   * did not match. If the character does not appear in the pattern, the
   * pattern can be shifted completely beyond the bad character. If the
   * character does occur in the pattern, the pattern can be shifted to
   * line the pattern up with the next occurrence of that character.
   * <p>
   * The good suffix shift is based on the idea that some subset on the right
   * side of the pattern has matched. When a bad character is found, the
   * pattern can be shifted right by the pattern length if the subset does
   * not occur again in pattern, or by the amount of distance to the
   * next occurrence of the subset in the pattern.
   *
   * Boyer-Moore search methods adapted from code by Amy Yu.
   */
  static class BnM extends Node {

    int[] buffer;
    int[] lastOcc;
    int[] optoSft;

    /**
     * Pre calculates arrays needed to generate the bad character
     * shift and the good suffix shift. Only the last seven bits
     * are used to see if chars match; This keeps the tables small
     * and covers the heavily used ASCII range, but occasionally
     * results in an aliased match for the bad character shift.
     */
    static Node optimize(Node node) {
      if (!(node instanceof Slice)) {
        return node;
      }

      int[] src = ((Slice) node).buffer;
      int patternLength = src.length;
      // The BM algorithm requires a bit of overhead;
      // If the pattern is short don't use it, since
      // a shift larger than the pattern length cannot
      // be used anyway.
      if (patternLength < 4) {
        return node;
      }
      int i, j, k;
      int[] lastOcc = new int[128];
      int[] optoSft = new int[patternLength];
      // Precalculate part of the bad character shift
      // It is a table for where in the pattern each
      // lower 7-bit value occurs
      for (i = 0; i < patternLength; i++) {
        lastOcc[src[i] & 0x7F] = i + 1;
      }
      // Precalculate the good suffix shift
      // i is the shift amount being considered
      NEXT:
      for (i = patternLength; i > 0; i--) {
        // j is the beginning index of suffix being considered
        for (j = patternLength - 1; j >= i; j--) {
          // Testing for good suffix
          if (src[j] == src[j - i]) {
            // src[j..len] is a good suffix
            optoSft[j - 1] = i;
          } else {
            // No match. The array has already been
            // filled up with correct values before.
            continue NEXT;
          }
        }
        // This fills up the remaining of optoSft
        // any suffix can not have larger shift amount
        // then its sub-suffix. Why???
        while (j > 0) {
          optoSft[--j] = i;
        }
      }
      // Set the guard value because of unicode compression
      optoSft[patternLength - 1] = 1;
      if (node instanceof SliceS) {
        return new BnMS(src, lastOcc, optoSft, node.next);
      }
      return new BnM(src, lastOcc, optoSft, node.next);
    }

    BnM(int[] src, int[] lastOcc, int[] optoSft, Node next) {
      this.buffer = src;
      this.lastOcc = lastOcc;
      this.optoSft = optoSft;
      this.next = next;
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int[] src = buffer;
      int patternLength = src.length;
      int last = matcher.to - patternLength;

      // Loop over all possible match positions in text
      NEXT:
      while (i <= last) {
        // Loop over pattern from right to left
        for (int j = patternLength - 1; j >= 0; j--) {
          int ch = seq.charAt(i + j);
          if (ch != src[j]) {
            // Shift search to the right by the maximum of the
            // bad character shift and the good suffix shift
            i += Math.max(j + 1 - lastOcc[ch & 0x7F], optoSft[j]);
            continue NEXT;
          }
        }
        // Entire pattern matched starting at i
        matcher.first = i;
        boolean ret = next.match(matcher, i + patternLength, seq);
        if (ret) {
          matcher.first = i;
          matcher.groups[0] = matcher.first;
          matcher.groups[1] = matcher.last;
          return true;
        }
        i++;
      }
      // BnM is only used as the leading node in the unanchored case,
      // and it replaced its Start() which always searches to the end
      // if it doesn't find what it's looking for, so hitEnd is true.
      matcher.hitEnd = true;
      return false;
    }

    boolean study(TreeInfo info) {
      info.minLength += buffer.length;
      info.maxValid = false;
      return next.study(info);
    }
  }

  /**
   * Supplementary support version of BnM(). Unpaired surrogates are
   * also handled by this class.
   */
  static final class BnMS extends BnM {

    int lengthInChars;

    BnMS(int[] src, int[] lastOcc, int[] optoSft, Node next) {
      super(src, lastOcc, optoSft, next);
      for (int x = 0; x < buffer.length; x++) {
        lengthInChars += Character.charCount(buffer[x]);
      }
    }

    boolean match(Matcher matcher, int i, CharSequence seq) {
      int[] src = buffer;
      int patternLength = src.length;
      int last = matcher.to - lengthInChars;

      // Loop over all possible match positions in text
      NEXT:
      while (i <= last) {
        // Loop over pattern from right to left
        int ch;
        for (int j = countChars(seq, i, patternLength), x = patternLength - 1;
            j > 0; j -= Character.charCount(ch), x--) {
          ch = Character.codePointBefore(seq, i + j);
          if (ch != src[x]) {
            // Shift search to the right by the maximum of the
            // bad character shift and the good suffix shift
            int n = Math.max(x + 1 - lastOcc[ch & 0x7F], optoSft[x]);
            i += countChars(seq, i, n);
            continue NEXT;
          }
        }
        // Entire pattern matched starting at i
        matcher.first = i;
        boolean ret = next.match(matcher, i + lengthInChars, seq);
        if (ret) {
          matcher.first = i;
          matcher.groups[0] = matcher.first;
          matcher.groups[1] = matcher.last;
          return true;
        }
        i += countChars(seq, i, 1);
      }
      matcher.hitEnd = true;
      return false;
    }
  }

///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////

  /**
   * This must be the very first initializer.
   */
  static Node accept = new Node();

  static Node lastAccept = new LastNode();

  private static class CharPropertyNames {

    static CharProperty charPropertyFor(String name) {
      CharPropertyFactory m = map.get(name);
      return m == null ? null : m.make();
    }

    private static abstract class CharPropertyFactory {

      abstract CharProperty make();
    }

    private static void defCategory(String name,
        final int typeMask) {
      map.put(name, new CharPropertyFactory() {
        CharProperty make() {
          return new Category(typeMask);
        }
      });
    }

    private static void defRange(String name,
        final int lower, final int upper) {
      map.put(name, new CharPropertyFactory() {
        CharProperty make() {
          return rangeFor(lower, upper);
        }
      });
    }

    private static void defCtype(String name,
        final int ctype) {
      map.put(name, new CharPropertyFactory() {
        CharProperty make() {
          return new Ctype(ctype);
        }
      });
    }

    private static abstract class CloneableProperty
        extends CharProperty implements Cloneable {

      public CloneableProperty clone() {
        try {
          return (CloneableProperty) super.clone();
        } catch (CloneNotSupportedException e) {
          throw new AssertionError(e);
        }
      }
    }

    private static void defClone(String name,
        final CloneableProperty p) {
      map.put(name, new CharPropertyFactory() {
        CharProperty make() {
          return p.clone();
        }
      });
    }

    private static final HashMap<String, CharPropertyFactory> map
        = new HashMap<>();

    static {
      // Unicode character property aliases, defined in
      // http://www.unicode.org/Public/UNIDATA/PropertyValueAliases.txt
      defCategory("Cn", 1 << Character.UNASSIGNED);
      defCategory("Lu", 1 << Character.UPPERCASE_LETTER);
      defCategory("Ll", 1 << Character.LOWERCASE_LETTER);
      defCategory("Lt", 1 << Character.TITLECASE_LETTER);
      defCategory("Lm", 1 << Character.MODIFIER_LETTER);
      defCategory("Lo", 1 << Character.OTHER_LETTER);
      defCategory("Mn", 1 << Character.NON_SPACING_MARK);
      defCategory("Me", 1 << Character.ENCLOSING_MARK);
      defCategory("Mc", 1 << Character.COMBINING_SPACING_MARK);
      defCategory("Nd", 1 << Character.DECIMAL_DIGIT_NUMBER);
      defCategory("Nl", 1 << Character.LETTER_NUMBER);
      defCategory("No", 1 << Character.OTHER_NUMBER);
      defCategory("Zs", 1 << Character.SPACE_SEPARATOR);
      defCategory("Zl", 1 << Character.LINE_SEPARATOR);
      defCategory("Zp", 1 << Character.PARAGRAPH_SEPARATOR);
      defCategory("Cc", 1 << Character.CONTROL);
      defCategory("Cf", 1 << Character.FORMAT);
      defCategory("Co", 1 << Character.PRIVATE_USE);
      defCategory("Cs", 1 << Character.SURROGATE);
      defCategory("Pd", 1 << Character.DASH_PUNCTUATION);
      defCategory("Ps", 1 << Character.START_PUNCTUATION);
      defCategory("Pe", 1 << Character.END_PUNCTUATION);
      defCategory("Pc", 1 << Character.CONNECTOR_PUNCTUATION);
      defCategory("Po", 1 << Character.OTHER_PUNCTUATION);
      defCategory("Sm", 1 << Character.MATH_SYMBOL);
      defCategory("Sc", 1 << Character.CURRENCY_SYMBOL);
      defCategory("Sk", 1 << Character.MODIFIER_SYMBOL);
      defCategory("So", 1 << Character.OTHER_SYMBOL);
      defCategory("Pi", 1 << Character.INITIAL_QUOTE_PUNCTUATION);
      defCategory("Pf", 1 << Character.FINAL_QUOTE_PUNCTUATION);
      defCategory("L", ((1 << Character.UPPERCASE_LETTER) |
          (1 << Character.LOWERCASE_LETTER) |
          (1 << Character.TITLECASE_LETTER) |
          (1 << Character.MODIFIER_LETTER) |
          (1 << Character.OTHER_LETTER)));
      defCategory("M", ((1 << Character.NON_SPACING_MARK) |
          (1 << Character.ENCLOSING_MARK) |
          (1 << Character.COMBINING_SPACING_MARK)));
      defCategory("N", ((1 << Character.DECIMAL_DIGIT_NUMBER) |
          (1 << Character.LETTER_NUMBER) |
          (1 << Character.OTHER_NUMBER)));
      defCategory("Z", ((1 << Character.SPACE_SEPARATOR) |
          (1 << Character.LINE_SEPARATOR) |
          (1 << Character.PARAGRAPH_SEPARATOR)));
      defCategory("C", ((1 << Character.CONTROL) |
          (1 << Character.FORMAT) |
          (1 << Character.PRIVATE_USE) |
          (1 << Character.SURROGATE))); // Other
      defCategory("P", ((1 << Character.DASH_PUNCTUATION) |
          (1 << Character.START_PUNCTUATION) |
          (1 << Character.END_PUNCTUATION) |
          (1 << Character.CONNECTOR_PUNCTUATION) |
          (1 << Character.OTHER_PUNCTUATION) |
          (1 << Character.INITIAL_QUOTE_PUNCTUATION) |
          (1 << Character.FINAL_QUOTE_PUNCTUATION)));
      defCategory("S", ((1 << Character.MATH_SYMBOL) |
          (1 << Character.CURRENCY_SYMBOL) |
          (1 << Character.MODIFIER_SYMBOL) |
          (1 << Character.OTHER_SYMBOL)));
      defCategory("LC", ((1 << Character.UPPERCASE_LETTER) |
          (1 << Character.LOWERCASE_LETTER) |
          (1 << Character.TITLECASE_LETTER)));
      defCategory("LD", ((1 << Character.UPPERCASE_LETTER) |
          (1 << Character.LOWERCASE_LETTER) |
          (1 << Character.TITLECASE_LETTER) |
          (1 << Character.MODIFIER_LETTER) |
          (1 << Character.OTHER_LETTER) |
          (1 << Character.DECIMAL_DIGIT_NUMBER)));
      defRange("L1", 0x00, 0xFF); // Latin-1
      map.put("all", new CharPropertyFactory() {
        CharProperty make() {
          return new All();
        }
      });

      // Posix regular expression character classes, defined in
      // http://www.unix.org/onlinepubs/009695399/basedefs/xbd_chap09.html
      defRange("ASCII", 0x00, 0x7F);   // ASCII
      defCtype("Alnum", ASCII.ALNUM);  // Alphanumeric characters
      defCtype("Alpha", ASCII.ALPHA);  // Alphabetic characters
      defCtype("Blank", ASCII.BLANK);  // Space and tab characters
      defCtype("Cntrl", ASCII.CNTRL);  // Control characters
      defRange("Digit", '0', '9');     // Numeric characters
      defCtype("Graph", ASCII.GRAPH);  // printable and visible
      defRange("Lower", 'a', 'z');     // Lower-case alphabetic
      defRange("Print", 0x20, 0x7E);   // Printable characters
      defCtype("Punct", ASCII.PUNCT);  // Punctuation characters
      defCtype("Space", ASCII.SPACE);  // Space characters
      defRange("Upper", 'A', 'Z');     // Upper-case alphabetic
      defCtype("XDigit", ASCII.XDIGIT); // hexadecimal digits

      // Java character properties, defined by methods in Character.java
      defClone("javaLowerCase", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isLowerCase(ch);
        }
      });
      defClone("javaUpperCase", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isUpperCase(ch);
        }
      });
      defClone("javaAlphabetic", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isAlphabetic(ch);
        }
      });
      defClone("javaIdeographic", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isIdeographic(ch);
        }
      });
      defClone("javaTitleCase", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isTitleCase(ch);
        }
      });
      defClone("javaDigit", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isDigit(ch);
        }
      });
      defClone("javaDefined", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isDefined(ch);
        }
      });
      defClone("javaLetter", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isLetter(ch);
        }
      });
      defClone("javaLetterOrDigit", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isLetterOrDigit(ch);
        }
      });
      defClone("javaJavaIdentifierStart", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isJavaIdentifierStart(ch);
        }
      });
      defClone("javaJavaIdentifierPart", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isJavaIdentifierPart(ch);
        }
      });
      defClone("javaUnicodeIdentifierStart", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isUnicodeIdentifierStart(ch);
        }
      });
      defClone("javaUnicodeIdentifierPart", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isUnicodeIdentifierPart(ch);
        }
      });
      defClone("javaIdentifierIgnorable", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isIdentifierIgnorable(ch);
        }
      });
      defClone("javaSpaceChar", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isSpaceChar(ch);
        }
      });
      defClone("javaWhitespace", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isWhitespace(ch);
        }
      });
      defClone("javaISOControl", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isISOControl(ch);
        }
      });
      defClone("javaMirrored", new CloneableProperty() {
        boolean isSatisfiedBy(int ch) {
          return Character.isMirrored(ch);
        }
      });
    }
  }

  /**
   * Creates a predicate which can be used to match a string.
   *
   * @return The predicate which can be used for matching on a string
   * @since 1.8
   */
  public Predicate<String> asPredicate() {
    return s -> matcher(s).find();
  }

  /**
   * Creates a stream from the given input sequence around matches of this
   * pattern.
   *
   * <p> The stream returned by this method contains each substring of the
   * input sequence that is terminated by another subsequence that matches
   * this pattern or is terminated by the end of the input sequence.  The
   * substrings in the stream are in the order in which they occur in the
   * input. Trailing empty strings will be discarded and not encountered in
   * the stream.
   *
   * <p> If this pattern does not match any subsequence of the input then
   * the resulting stream has just one element, namely the input sequence in
   * string form.
   *
   * <p> When there is a positive-width match at the beginning of the input
   * sequence then an empty leading substring is included at the beginning
   * of the stream. A zero-width match at the beginning however never produces
   * such empty leading substring.
   *
   * <p> If the input sequence is mutable, it must remain constant during the
   * execution of the terminal stream operation.  Otherwise, the result of the
   * terminal stream operation is undefined.
   *
   * @param input The character sequence to be split
   * @return The stream of strings computed by splitting the input around matches of this pattern
   * @see #split(CharSequence)
   * @since 1.8
   */
  public Stream<String> splitAsStream(final CharSequence input) {
    class MatcherIterator implements Iterator<String> {

      private final Matcher matcher;
      // The start position of the next sub-sequence of input
      // when current == input.length there are no more elements
      private int current;
      // null if the next element, if any, needs to obtained
      private String nextElement;
      // > 0 if there are N next empty elements
      private int emptyElementCount;

      MatcherIterator() {
        this.matcher = matcher(input);
      }

      public String next() {
        if (!hasNext()) {
          throw new NoSuchElementException();
        }

        if (emptyElementCount == 0) {
          String n = nextElement;
          nextElement = null;
          return n;
        } else {
          emptyElementCount--;
          return "";
        }
      }

      public boolean hasNext() {
        if (nextElement != null || emptyElementCount > 0) {
          return true;
        }

        if (current == input.length()) {
          return false;
        }

        // Consume the next matching element
        // Count sequence of matching empty elements
        while (matcher.find()) {
          nextElement = input.subSequence(current, matcher.start()).toString();
          current = matcher.end();
          if (!nextElement.isEmpty()) {
            return true;
          } else if (current > 0) { // no empty leading substring for zero-width
            // match at the beginning of the input
            emptyElementCount++;
          }
        }

        // Consume last matching element
        nextElement = input.subSequence(current, input.length()).toString();
        current = input.length();
        if (!nextElement.isEmpty()) {
          return true;
        } else {
          // Ignore a terminal sequence of matching empty elements
          emptyElementCount = 0;
          nextElement = null;
          return false;
        }
      }
    }
    return StreamSupport.stream(Spliterators.spliteratorUnknownSize(
        new MatcherIterator(), Spliterator.ORDERED | Spliterator.NONNULL), false);
  }
}
